Right now the editor sets the selection node bg and label ids, but doesn't change the fg id before propagation. This means that if the selection node has an existing fg id it should not change.

Testing this now I could not replicate the issue. Here is what I did:

• download MRHead and DTIBrain
• link views and put MR in background and DTI in fg with 50% fade
• enter editor and create label map
• draw

The fg does not change.

What's different in your case?

Steve, this appears to be reproducible with the sample data. I attached are screenshots with slice configurations before entering Editor, and after entering Editor and accepting MRBrainTumor2 as master volume. I have nothing else in the scene, and I loaded the volumes through Sample data.

So I guess the solution would be to add different methods for bg, fg, and lb to [1] so the editor could control the layers independently.

[1] vtkMRMLApplicationLogic::PropagateVolumeSelection

Workaround: save the scene before entering Editor, enter Editor, load the scene.

Correction: worked in one case.

Workaround that works: comment out all occurrences of PropagateVolumeSelection() in
Slicer_INSTALL_DIR/lib/Slicer-4.3/qt-scripted-modules/EditorLib/HelperBox.py

The new Segment Editor does not have this behavior, it should be used instead of the Editor. The Segment Editor only hides foreground and labelmap volumes when the master volume is changed.