Ok, I posted once before about this & then I mistakenly thought I was able to repeat the problem but was actaully activating an unrelated feature. So, the problem is still the same: when I’m using the final WIP, several times a day the perspective viewport goes into a weird mode. The view continues to be a perspective view, but the mouse no longer does what it’s supposed to do. My RMB becomes Zoom instead of Rotate, and I can’t select objects in the viewport or change it to anything else. And, Shift+RMB becomes Rotate and CTRL+RMB becomes Pan. If I click out of Rhino and into any other program, then back to Rhino, that fixes it. But nothing in Rhino fixes it. Enjoy the video that I had to take with my phone (because activating a screen-capture program makes Rhino go back to regular behavior.) Please note that at the end of the video I open Irfanview on my other screen, which fixes the Rhino problem.