Switching between extensions causes no observer message

[rbumm]

C:\Users\Rudolf\AppData\Local\NA-MIC\Slicer 5.0.3\bin\Python\slicer\util.py:2486: UserWarning: does not have observer
  warn('does not have observer')

@lassoan do you have a suggestion on how to fix this? Thanks.

And maybe comment on the automatic window/level switch (still hardcoded) if a user runs Lung CT Segmenter? I almost always have to make this switch and it would save a click and UI option space.