diff --git a/scripts/tools/blender_obj.py b/scripts/tools/blender_obj.py
index c03a525fae49..b0461eea6646 100644
--- a/scripts/tools/blender_obj.py
+++ b/scripts/tools/blender_obj.py
@@ -67,8 +67,9 @@ def convert_to_obj(in_file: str, out_file: str, save_usd: bool = False):
     if not out_file.endswith(".obj"):
         out_file += ".obj"
     # create directory if it doesn't exist for destination file
-    if not os.path.exists(os.path.dirname(out_file)):
-        os.makedirs(os.path.dirname(out_file), exist_ok=True)
+    out_dir = os.path.dirname(out_file)
+    if out_dir and not os.path.exists(out_dir):
+        os.makedirs(out_dir, exist_ok=True)
     # reset scene to empty
     bpy.ops.wm.read_factory_settings(use_empty=True)
     # load object into scene
@@ -86,8 +87,8 @@ def convert_to_obj(in_file: str, out_file: str, save_usd: bool = False):
     )
     # save it as usd as well
     if save_usd:
-        out_file = out_file.replace("obj", "usd")
-        bpy.ops.wm.usd_export(filepath=out_file, check_existing=False)
+        usd_file = os.path.splitext(out_file)[0] + ".usd"
+        bpy.ops.wm.usd_export(filepath=usd_file, check_existing=False)
 
 
 if __name__ == "__main__":
diff --git a/scripts/tools/process_meshes_to_obj.py b/scripts/tools/process_meshes_to_obj.py
index 2e5371225bae..74e128e29d03 100644
--- a/scripts/tools/process_meshes_to_obj.py
+++ b/scripts/tools/process_meshes_to_obj.py
@@ -34,22 +34,27 @@ def parse_cli_args():
     return args_cli
 
 
-def run_blender_convert2obj(in_file: str, out_file: str):
-    """Calls the python script using `subprocess` to perform processing of mesh file.
+def run_blender_convert2obj(in_file: str, out_file: str) -> None:
+    """Call the Blender script to convert a mesh file to OBJ.
 
     Args:
         in_file: Input mesh file.
         out_file: Output obj file.
+
+    Raises:
+        FileNotFoundError: If the Blender executable cannot be found on ``PATH``.
+        subprocess.CalledProcessError: If Blender exits with a non-zero status.
     """
+    if BLENDER_EXE_PATH is None:
+        raise FileNotFoundError("Unable to find the Blender executable on PATH.")
+
     # resolve for python file
     tools_dirname = os.path.dirname(os.path.abspath(__file__))
     script_file = os.path.join(tools_dirname, "blender_obj.py")
-    # complete command
-    command_exe = f"{BLENDER_EXE_PATH} --background --python {script_file} -- -i {in_file} -o {out_file}"
-    # break command into list
-    command_exe_list = command_exe.split(" ")
-    # run command
-    subprocess.run(command_exe_list)
+    # build the argument list directly so paths containing whitespace remain single arguments
+    command_exe = [BLENDER_EXE_PATH, "--background", "--python", script_file, "--", "-i", in_file, "-o", out_file]
+    # run command and surface conversion failures to the caller
+    subprocess.run(command_exe, check=True)
 
 
 def convert_meshes(source_folders: list[str], destination_folders: list[str]):
diff --git a/scripts/tools/test/test_blender_obj.py b/scripts/tools/test/test_blender_obj.py
new file mode 100644
index 000000000000..fbac86c978e5
--- /dev/null
+++ b/scripts/tools/test/test_blender_obj.py
@@ -0,0 +1,50 @@
+# Copyright (c) 2022-2026, The Isaac Lab Project Developers (https://github.com/isaac-sim/IsaacLab/blob/main/CONTRIBUTORS.md).
+# All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+
+import importlib
+import sys
+from unittest.mock import Mock
+
+import pytest
+
+pytestmark = pytest.mark.unit
+
+
+@pytest.fixture
+def blender_obj_module(monkeypatch):
+    fake_bpy = Mock()
+    monkeypatch.setitem(sys.modules, "bpy", fake_bpy)
+    sys.modules.pop("scripts.tools.blender_obj", None)
+    return importlib.import_module("scripts.tools.blender_obj"), fake_bpy
+
+
+def test_convert_to_obj_supports_current_directory_output(blender_obj_module, tmp_path):
+    blender_obj, fake_bpy = blender_obj_module
+    input_path = tmp_path / "input.stl"
+    input_path.touch()
+
+    blender_obj.convert_to_obj(str(input_path), "robot.obj")
+
+    fake_bpy.ops.export_scene.obj.assert_called_once_with(
+        filepath="robot.obj",
+        check_existing=False,
+        axis_forward="Y",
+        axis_up="Z",
+        global_scale=1,
+        path_mode="RELATIVE",
+    )
+
+
+def test_save_usd_replaces_only_output_extension(blender_obj_module, tmp_path):
+    blender_obj, fake_bpy = blender_obj_module
+    input_path = tmp_path / "input.stl"
+    input_path.touch()
+    output_path = tmp_path / "objects" / "robot.obj"
+
+    blender_obj.convert_to_obj(str(input_path), str(output_path), save_usd=True)
+
+    fake_bpy.ops.wm.usd_export.assert_called_once_with(
+        filepath=str(output_path.with_suffix(".usd")), check_existing=False
+    )
diff --git a/scripts/tools/test/test_process_meshes_to_obj.py b/scripts/tools/test/test_process_meshes_to_obj.py
new file mode 100644
index 000000000000..da08cfde2e63
--- /dev/null
+++ b/scripts/tools/test/test_process_meshes_to_obj.py
@@ -0,0 +1,37 @@
+# Copyright (c) 2022-2026, The Isaac Lab Project Developers (https://github.com/isaac-sim/IsaacLab/blob/main/CONTRIBUTORS.md).
+# All rights reserved.
+#
+# SPDX-License-Identifier: BSD-3-Clause
+
+from pathlib import Path
+from unittest.mock import Mock
+
+import pytest
+
+from scripts.tools import process_meshes_to_obj
+
+pytestmark = pytest.mark.unit
+
+
+def test_blender_command_preserves_paths_with_spaces(monkeypatch):
+    blender_path = "/path to/blender"
+    input_path = "/path to/input mesh.stl"
+    output_path = "/path to/output mesh.obj"
+    run_mock = Mock()
+    monkeypatch.setattr(process_meshes_to_obj, "BLENDER_EXE_PATH", blender_path)
+    monkeypatch.setattr(process_meshes_to_obj.subprocess, "run", run_mock)
+
+    process_meshes_to_obj.run_blender_convert2obj(input_path, output_path)
+
+    script_path = str(Path(process_meshes_to_obj.__file__).with_name("blender_obj.py"))
+    run_mock.assert_called_once_with(
+        [blender_path, "--background", "--python", script_path, "--", "-i", input_path, "-o", output_path],
+        check=True,
+    )
+
+
+def test_blender_conversion_requires_executable(monkeypatch):
+    monkeypatch.setattr(process_meshes_to_obj, "BLENDER_EXE_PATH", None)
+
+    with pytest.raises(FileNotFoundError, match="Blender executable"):
+        process_meshes_to_obj.run_blender_convert2obj("input.stl", "output.obj")
diff --git a/source/isaaclab/changelog.d/fix-newton-actuators-multi-asset.fixed.rst b/source/isaaclab/changelog.d/fix-newton-actuators-multi-asset.fixed.rst
new file mode 100644
index 000000000000..c2a86103e533
--- /dev/null
+++ b/source/isaaclab/changelog.d/fix-newton-actuators-multi-asset.fixed.rst
@@ -0,0 +1,4 @@
+* Fixed Newton-native actuators driving only the first asset of a multi-asset scene. ``NewtonActuator`` prims
+  were authored on the first prim matching the articulation path, so every other spawned asset
+  imported into the Newton model without actuators and its joints received no torque. They are now authored on
+  every matching articulation.
diff --git a/source/isaaclab/changelog.d/sylvesterkaczmarek-action-descriptor-stdout.fixed.rst b/source/isaaclab/changelog.d/sylvesterkaczmarek-action-descriptor-stdout.fixed.rst
new file mode 100644
index 000000000000..be83f85d428b
--- /dev/null
+++ b/source/isaaclab/changelog.d/sylvesterkaczmarek-action-descriptor-stdout.fixed.rst
@@ -0,0 +1 @@
+* Removed stray debug output from action IO descriptor export.
diff --git a/source/isaaclab/changelog.d/sylvesterkaczmarek-dump-yaml-yml-extension.fixed.rst b/source/isaaclab/changelog.d/sylvesterkaczmarek-dump-yaml-yml-extension.fixed.rst
new file mode 100644
index 000000000000..23ddcc764c4c
--- /dev/null
+++ b/source/isaaclab/changelog.d/sylvesterkaczmarek-dump-yaml-yml-extension.fixed.rst
@@ -0,0 +1,2 @@
+* Fixed ``dump_yaml()`` to preserve existing ``.yml`` and case-insensitive YAML file extensions instead of appending
+  ``.yaml``.
diff --git a/source/isaaclab/changelog.d/sylvesterkaczmarek-fix-circular-buffer-uninitialized-buffer.fixed.rst b/source/isaaclab/changelog.d/sylvesterkaczmarek-fix-circular-buffer-uninitialized-buffer.fixed.rst
new file mode 100644
index 000000000000..abd7fe5e32d2
--- /dev/null
+++ b/source/isaaclab/changelog.d/sylvesterkaczmarek-fix-circular-buffer-uninitialized-buffer.fixed.rst
@@ -0,0 +1,2 @@
+* Fixed ``CircularBuffer.buffer`` raising an implementation-level PyTorch error when accessed before the first
+  ``append()`` by reporting a clear ``RuntimeError`` instead.
diff --git a/source/isaaclab/isaaclab/managers/action_manager.py b/source/isaaclab/isaaclab/managers/action_manager.py
index f118c209be46..0a7bf089b8f3 100644
--- a/source/isaaclab/isaaclab/managers/action_manager.py
+++ b/source/isaaclab/isaaclab/managers/action_manager.py
@@ -310,7 +310,6 @@ def _collect_io_descriptors(self) -> list[dict[str, Any]]:
         for item in data:
             name = item.pop("name")
             formatted_item = {"name": name, "extras": item.pop("extras")}
-            print(item["export"])
             if not item.pop("export"):
                 continue
             for k, v in item.items():
diff --git a/source/isaaclab/isaaclab/sim/schemas/schemas_actuators.py b/source/isaaclab/isaaclab/sim/schemas/schemas_actuators.py
index e7dcf379e595..67fbef60c571 100644
--- a/source/isaaclab/isaaclab/sim/schemas/schemas_actuators.py
+++ b/source/isaaclab/isaaclab/sim/schemas/schemas_actuators.py
@@ -169,8 +169,8 @@ def define_actuator_properties(
 
     Args:
         prim_path: Root prim path of the articulation (e.g.
-            ``"/World/Env_0/Robot"``). May contain a regex pattern; the
-            first matching prim is used.
+            ``"/World/Env_0/Robot"``). May contain a regex pattern; every matching prim is
+            authored, because a multi-asset spawner creates a distinct articulation per match.
         actuator_cfgs: Mapping of group name to
             :class:`~isaaclab.actuators.ActuatorBaseCfg`.
         stage: USD stage to author on. When ``None``, the current stage
@@ -186,18 +186,16 @@ def define_actuator_properties(
     if sim_cfg is None or not sim_cfg.use_newton_actuators:
         return
 
-    from ..utils.queries import find_first_matching_prim  # noqa: PLC0415
+    from ..utils.queries import find_matching_prims  # noqa: PLC0415
     from ..utils.stage import get_current_stage  # noqa: PLC0415
 
     if stage is None:
         stage = get_current_stage()
 
-    first_prim = find_first_matching_prim(prim_path)
-    if first_prim is None:
-        return
-    articulation_prim_path = str(first_prim.GetPath())
-
-    author_actuator_prims(stage, articulation_prim_path, actuator_cfgs)
+    # Each match is a separately spawned articulation. A multi-asset spawner creates one per asset
+    # before cloning, and the Newton builder only sees actuators authored on the prim it imports.
+    for prim in find_matching_prims(prim_path, stage):
+        author_actuator_prims(stage, str(prim.GetPath()), actuator_cfgs)
 
 
 def author_actuator_prims(
diff --git a/source/isaaclab/isaaclab/utils/buffers/circular_buffer.py b/source/isaaclab/isaaclab/utils/buffers/circular_buffer.py
index 985a9d5ed2ab..2368336ed686 100644
--- a/source/isaaclab/isaaclab/utils/buffers/circular_buffer.py
+++ b/source/isaaclab/isaaclab/utils/buffers/circular_buffer.py
@@ -108,7 +108,12 @@ def buffer(self) -> torch.Tensor:
         Returns:
             Complete circular buffer with most recent entry at the end and oldest entry at the beginning of
             dimension 1. The shape is [batch_size, max_length, data.shape[1:]].
+
+        Raises:
+            RuntimeError: If no data has been appended yet.
         """
+        if self._buffer is None:
+            raise RuntimeError("The buffer is empty. Please append data before retrieving.")
         if self._stack_dim_internal is None:
             return torch.transpose(self._buffer, dim0=0, dim1=1)
         return torch.movedim(self._buffer, source=self._stack_dim_internal, destination=1)
diff --git a/source/isaaclab/isaaclab/utils/io/yaml.py b/source/isaaclab/isaaclab/utils/io/yaml.py
index 82214c468fad..e0c3405503c2 100644
--- a/source/isaaclab/isaaclab/utils/io/yaml.py
+++ b/source/isaaclab/isaaclab/utils/io/yaml.py
@@ -43,7 +43,7 @@ def dump_yaml(filename: str, data: dict | object, sort_keys: bool = False):
         sort_keys: Whether to sort the keys in the output file. Defaults to False.
     """
     # check ending
-    if not filename.endswith("yaml"):
+    if not filename.lower().endswith((".yaml", ".yml")):
         filename += ".yaml"
     # create directory
     directory = os.path.dirname(filename)
diff --git a/source/isaaclab/test/actuators/test_newton_adapter.py b/source/isaaclab/test/actuators/test_newton_adapter.py
index 52841965c6ce..21fac108251a 100644
--- a/source/isaaclab/test/actuators/test_newton_adapter.py
+++ b/source/isaaclab/test/actuators/test_newton_adapter.py
@@ -6,6 +6,7 @@
 """Tests for the PhysX-side Newton actuator adapter."""
 
 from pathlib import Path
+from types import SimpleNamespace
 
 import numpy as np
 import pytest
@@ -16,8 +17,12 @@
 
 from isaaclab.actuators import ActuatorBaseCfg, DCMotor, DCMotorCfg, DelayedPDActuatorCfg, RemotizedPDActuatorCfg
 from isaaclab.actuators.newton import NewtonActuatorAdapter
-from isaaclab.sim import SimulationCfg
-from isaaclab.sim.schemas.schemas_actuators import author_actuator_prims, resave_checkpoint_with_metadata
+from isaaclab.sim import SimulationCfg, SimulationContext
+from isaaclab.sim.schemas.schemas_actuators import (
+    author_actuator_prims,
+    define_actuator_properties,
+    resave_checkpoint_with_metadata,
+)
 from isaaclab.utils import configclass
 
 _JOINT_NAMES = ["pd_a", "pd_b", "dc_a", "dc_b", "remote_a", "remote_b"]
@@ -280,3 +285,29 @@ def test_schema_authoring_accepts_supported_public_actuator_alias():
     author_actuator_prims(stage, "/World/Robot", {"public_alias": cfg})
 
     assert stage.GetPrimAtPath("/World/Robot/public_alias_pd_a_actuator").IsValid()
+
+
+def test_define_actuator_properties_authors_every_spawned_articulation(monkeypatch):
+    """A multi-asset spawner creates one articulation per match, and each needs its own actuator prims."""
+    stage = Usd.Stage.CreateInMemory()
+    robot_paths = [f"/World/envs/env_{index}/Robot" for index in range(3)]
+    for robot_path in robot_paths:
+        UsdGeom.Xform.Define(stage, robot_path)
+        body = UsdGeom.Xform.Define(stage, f"{robot_path}/body")
+        UsdPhysics.RigidBodyAPI.Apply(body.GetPrim())
+        joint = UsdPhysics.RevoluteJoint.Define(stage, f"{robot_path}/pd_a")
+        joint.CreateBody1Rel().SetTargets([body.GetPath()])
+    monkeypatch.setattr(
+        SimulationContext,
+        "instance",
+        staticmethod(lambda: SimpleNamespace(cfg=SimpleNamespace(use_newton_actuators=True))),
+    )
+    cfg = DelayedPDActuatorCfg(
+        joint_names_expr=["pd_a"], stiffness=11.0, damping=1.5, actuator_effort_limit=21.0, max_delay=2
+    )
+
+    define_actuator_properties(r"/World/envs/env_.*/Robot", {"pd": cfg}, stage=stage)
+
+    for robot_path in robot_paths:
+        actuators = [prim for prim in stage.Traverse() if prim.GetTypeName() == "NewtonActuator"]
+        assert any(str(prim.GetPath()).startswith(robot_path + "/") for prim in actuators), robot_path
diff --git a/source/isaaclab/test/performance/test_robot_load_performance.py b/source/isaaclab/test/performance/test_robot_load_performance.py
index 18da105f91fb..517434c561b9 100644
--- a/source/isaaclab/test/performance/test_robot_load_performance.py
+++ b/source/isaaclab/test/performance/test_robot_load_performance.py
@@ -13,11 +13,8 @@
 
 launch_test_simulation()
 
-import numpy as np
 import pytest
-from isaaclab_physx.cloner import physx_replicate
 
-import isaaclab.sim.utils as sim_utils
 from isaaclab import cloner
 from isaaclab.assets import Articulation
 from isaaclab.sim import build_simulation_context
@@ -47,33 +44,13 @@ def test_robot_load_performance(test_config, device):
     """Test robot load time."""
     with build_simulation_context(device=device) as sim:
         sim._app_control_on_stop_handle = None
-        stage = sim_utils.get_current_stage()
-
-        # Generate grid positions for environments
-        positions, _ = cloner.grid_transforms(NUM_ENVS, SPACING)
-
-        # Create environment prims using USD replicate
-        env_paths = [f"/World/Robots_{i}" for i in range(NUM_ENVS)]
-        stage.DefinePrim(env_paths[0], "Xform")
-        cloner.usd_replicate(
-            stage=stage,
-            sources=[env_paths[0]],
-            destinations=["/World/Robots_{}"],
-            env_ids=np.arange(NUM_ENVS, dtype=np.int64),
-            positions=positions,
-        )
-
-        # Replicate physics - mapping is (num_sources, num_envs) bool mask
-        physx_replicate(
-            stage=stage,
-            sources=[env_paths[0]],
-            destinations=["/World/Robots_{}"],
-            env_ids=np.arange(NUM_ENVS, dtype=np.int64),
-            mapping=np.ones((1, NUM_ENVS), dtype=np.bool_),  # 1 source -> all envs
-        )
 
         with Timer(f"{test_config['name']} load time for device {device}") as timer:
-            robot = Articulation(replace(test_config["robot_cfg"], prim_path="/World/Robots_[^/]*/Robot"))  # noqa: F841
+            cfg = replace(test_config["robot_cfg"], prim_path="{ENV_REGEX_NS}/Robot")
+            plan = cloner.clone_plan_from_env_0(cloner.CloneCfg(), (cfg,), NUM_ENVS, SPACING)
+            robot = Articulation(cfg)
+            cloner.replicate(plan)
             sim.reset()
             elapsed_time = timer.time_elapsed
+        assert robot.num_instances == NUM_ENVS
         assert elapsed_time <= test_config["expected_load_time"]
diff --git a/source/isaaclab/test/utils/test_circular_buffer.py b/source/isaaclab/test/utils/test_circular_buffer.py
index 5b51f9fa5f9b..41f59ca04b2f 100644
--- a/source/isaaclab/test/utils/test_circular_buffer.py
+++ b/source/isaaclab/test/utils/test_circular_buffer.py
@@ -113,6 +113,9 @@ def test_empty_buffer_access(circular_buffer):
     with pytest.raises(RuntimeError):
         circular_buffer[torch.tensor([0, 0, 0], device=circular_buffer.device)]
 
+    with pytest.raises(RuntimeError, match="append data"):
+        _ = circular_buffer.buffer
+
 
 def test_invalid_batch_size(circular_buffer):
     """Test appending data with an invalid batch size."""
@@ -148,6 +151,11 @@ def test_return_buffer_prop(circular_buffer):
     """Test retrieving the whole buffer for correct size and contents.
     Returning the whole buffer should have the shape [batch_size,max_len,data.shape[1:]]
     """
+    data = torch.tensor([[1, 2], [3, 4], [5, 6]], device=circular_buffer.device)
+    circular_buffer.append(data)
+    expected = data.unsqueeze(1).repeat(1, circular_buffer.max_length, 1)
+    torch.testing.assert_close(circular_buffer.buffer, expected)
+
     num_overflow = 2
     for i in range(circular_buffer.max_length + num_overflow):
         data = torch.tensor([[i]], device=circular_buffer.device).repeat(3, 2)
diff --git a/source/isaaclab/test/utils/test_yaml_io.py b/source/isaaclab/test/utils/test_yaml_io.py
index 6e76aef2416f..185d367d1867 100644
--- a/source/isaaclab/test/utils/test_yaml_io.py
+++ b/source/isaaclab/test/utils/test_yaml_io.py
@@ -25,3 +25,14 @@ def test_dump_yaml_adds_extension_in_current_working_directory(monkeypatch, tmp_
     dump_yaml("config", {"value": 42})
 
     assert (tmp_path / "config.yaml").is_file()
+
+
+@pytest.mark.parametrize("filename", ["config.yml", "config.YML"])
+def test_dump_yaml_preserves_yml_extension(monkeypatch, tmp_path, filename):
+    monkeypatch.chdir(tmp_path)
+
+    dump_yaml(filename, {"value": 42})
+
+    assert (tmp_path / filename).is_file()
+    assert not (tmp_path / f"{filename}.yaml").exists()
+    assert load_yaml(filename) == {"value": 42}