Thanks Capnm- z-depth ordering seems to describe the problem- and after playing some more it is independent of the mirror.

Is this already in the daily build?

Awesome- Thanks for looking at this Antonio

Perhaps 'occluded" has a specific technical meaning- but I was using it to mean "hidden" or obstructed- that GP strokes were not being hidden by geometry.
Hopefully the attached video will give you a clearer understanding of the behavior I was referring to. Many concept designers are going to sketch out surface detail on blocked in geometry- the current behavior will interfere with that workflow.