Hi peterlukejenkins,
I'm having the same problem here. We recently migrated from 2008 to 2012 and the problem started. We're working with referenced viewports (design layer viewports) a lot, and that seems to affect that behavior.
I noticed that it's significantly slower to enter/ exit groups if a referenced viewport is visible in the drawing.
If the viewport is part of another layer than the one I am working on (on which e.g. the group is drawn I want to enter/exit), switching is slow.
If the viewport is part of the same layer as the group, it gets EXTREMELY slow. There is a noticable difference.
Anyone having the same problems, or even better a solution?
Thanks