Hi Michael,

I've tried it again, and I consistently have to left-click (tap on tablet with pen tip) before I can pan a viewport with MMB (assigned to one of my Wacom pen side-buttons). This might be a Wacom pen only issue, I can't test that because I only work with the Wacom tablet for navigation, and I've got no mouse anymore.

You'd think though that if a pen-assigned RMB does work for panning as soon as you hover over a viewport, a similarly pen-assigned MMB should (be able to) behave the same way.