The check for using 2d or 3d versions of the glyphs is done (mostly) in the Is2DDisplayableManager method that uses:
this->m_SliceNode != NULL
to check if there's a slice node associated with the displayable manager. That check will need to be expanded for the compare view case and places in the code that still do the check for a slice node directly need to use the Is2DDisplayableManager call.

Jim, could you take a look? The compare view does not seem to display correctly currently.

This seems to be resolved, Ron are you still seeing this behaviour?

yes, I still see this behaviour

Ron: I can't reproduce it, which layout are you using?

compareview, 2 strips, slicer mac nightly, 3-28

This might be reproducible if the layouts change such that the number of slice viewers goes down and then up again. Check the order of operations when a slice viewer that was unmapped is remapped as a compare viewer.

I just tested this on the Mac since JC recently changed how the annotations detect 2D vs 3D.

This is working on my machine.

Ron, do you still see the issue?

This issue is gone. I can drag a fiducial on the red slice, but not on the compareviewer

This is no longer an issue.

Other tickets are addressing the interaction of fiducials and the lightbox.