This is going to be a short one – I spent most of the day working on dead-end attempts at fixing that rendering problem, which is more than just a rendering problem, and affects more than just Drawing…
There is some accompanying weirdness in the way mouse events are handled even when I’ve fixed the way the screen looks. If the mouse is clicked over the area where the stray rendering would’ve been, then the mouse gets passed on to the wrong widget. Strangely, the problem doesn’t manifest until the mouse is clicked (mouseover behaves as it should). My suspicion is that it’s a Coin3D-related issue.
A few months ago, I made some modifications to Sketcher that never got committed (to use keyboard modifier keys for selectively disabling snap-to-grid and automatic constraint creation), I think those modifications involve a similar code path to what mouse events are using here. Brain is too fried to look at that today, I ran into some snags getting a debugger setup, and I need to go buy some groceries for tomorrow’s Fiordland trip!
At this point, I think the next thing I’ll try is stepping through the path a mouse click event takes to see if there’s an obvious problem. If that doesn’t lead to a solution, then either continue on to something else, or construct a minimal test case outside of FreeCAD.
Back in a few days, and thanks for all the support!