diff --git a/datalab/tests/webapi_extra_test.py b/datalab/tests/webapi_extra_test.py
index b8e7093ab..9fd8e96f8 100644
--- a/datalab/tests/webapi_extra_test.py
+++ b/datalab/tests/webapi_extra_test.py
@@ -145,6 +145,42 @@ def test_workspace_adapter_resolves_uuid_and_rejects_ambiguous_titles() -> None:
     image_panel.SIG_OBJECT_REMOVED.emit.assert_called_once_with()
 
 
+def test_workspace_adapter_uploaded_copy_gets_a_new_identity() -> None:
+    """An object downloaded then uploaded under another name is a new object.
+
+    Regression: the copy carried the UUID of the original object, the panel
+    refused it and showed the error in a modal dialog, so that the request hung
+    until the main-thread timeout (DataLab-Kernel ``rename``).
+    """
+    signal = _make_signal("Original", n=10)
+    signal_panel = make_panel([signal])
+
+    def add_object(obj: DataObject) -> None:
+        if get_uuid(obj) in [get_uuid(other) for other in signal_panel.objmodel]:
+            raise ValueError("Object already in panel")
+        signal_panel.objmodel.append(obj)
+
+    signal_panel._add_object = add_object  # pylint: disable=protected-access
+    adapter = WorkspaceAdapter(
+        SimpleNamespace(signalpanel=signal_panel, imagepanel=make_panel([]))
+    )
+    copy = adapter.get_object(get_uuid(signal))
+    assert get_uuid(copy) == get_uuid(signal)
+    copy.title = "Renamed"
+    adapter.add_object(copy)
+    assert len(signal_panel.objmodel) == 2
+    assert get_uuid(signal_panel.objmodel[1]) != get_uuid(signal)
+    assert get_uuid(signal) == get_uuid(signal_panel.objmodel[0])
+
+    # Errors of the panel are raised to the caller, not shown in a dialog
+    def failing_add(_obj: DataObject) -> None:
+        raise ValueError("refused")
+
+    signal_panel._add_object = failing_add  # pylint: disable=protected-access
+    with pytest.raises(ValueError, match="refused"):
+        adapter.add_object(_make_signal("Other"))
+
+
 # =============================================================================
 # Serialization helpers — _to_python_scalar
 # =============================================================================
diff --git a/datalab/webapi/adapter.py b/datalab/webapi/adapter.py
index de3a156d7..16431c0f6 100644
--- a/datalab/webapi/adapter.py
+++ b/datalab/webapi/adapter.py
@@ -34,7 +34,7 @@
 
 from qtpy.QtCore import QCoreApplication, QObject, QThread, Signal, Slot
 
-from datalab.objectmodel import UUID_REGEX, get_uuid
+from datalab.objectmodel import UUID_REGEX, get_uuid, set_uuid
 
 if TYPE_CHECKING:
     from sigima.objects import ImageObj, SignalObj
@@ -342,7 +342,13 @@ def add_object(self, obj: DataObject, overwrite: bool = False) -> None:
         self._add_object_sync(obj)
 
     def _add_object_sync(self, obj: DataObject) -> None:
-        """Add object (called from main thread or marshaled via executor)."""
+        """Add object (called from main thread or marshaled via executor).
+
+        The object is a new one: it gets its own identity, whatever UUID its
+        metadata carry (e.g. an object downloaded from the API and uploaded
+        again under another name). Errors are raised to the caller, never shown
+        in a dialog.
+        """
         obj_type = type(obj).__name__
 
         if obj_type == "SignalObj":
@@ -352,8 +358,9 @@ def _add_object_sync(self, obj: DataObject) -> None:
         else:
             raise TypeError(f"Unsupported object type: {obj_type}")
 
-        # Use executor to run on main thread if necessary
-        self._executor.run_on_main_thread(lambda: panel.add_object(obj))
+        set_uuid(obj)
+        # pylint: disable-next=protected-access
+        self._executor.run_on_main_thread(lambda: panel._add_object(obj))
 
     def remove_object(self, name: str) -> None:
         """Remove an object from the workspace.