Viewport reference grid rendered into the first captured frame intermittently #887

Description

Summary. With a fresh stage and rep.orchestrator.step() (no rt_subframes), the first frame written by a BasicWriter intermittently contains the viewport's reference grid and the red/green world-axis lines. Later frames are clean.

Reproduce. Run NVIDIA's own example, unmodified, several times:

docker run --rm --gpus all -e ACCEPT_EULA=Y -e PRIVACY_CONSENT=Y \
  --entrypoint /isaac-sim/python.sh nvcr.io/nvidia/isaac-sim:6.1.0 \
  -u /isaac-sim/standalone_examples/api/isaacsim.replicator.examples/sdg_getting_started_01.py

and inspect _out_basic_writer/rgb_0000.png.

Observed. The grid and axis lines appeared in rgb_0000.png in 4 of 6 runs. On 6.0.1, starting from a fresh stage was enough to keep it out.

Expected. No viewport overlays in captured data.

Workaround. Disable the grid before rendering (0 of 7 runs showed it afterwards):

carb.settings.get_settings().set_bool("/app/viewport/grid/enabled", False)
carb.settings.get_settings().set_bool("/app/viewport/defaults/guide/grid/visible", False)

Isaac Sim version

6.1.0

Operating System (OS)

Ubuntu 24.04

GPU Name

RTX 3070

GPU Driver and CUDA versions

580.178.04 13.0

Logs

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Additional information

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