Hmm.
The next time it happens can you run these in the chat window and tell me the results?
Code:
/script d(SCENE_MANAGER.numTopLevelShown)
Code:
/script d("Showing Toplevels:\n"); for topLevel in pairs(SCENE_MANAGER.topLevelWindows) do if not topLevel:IsHidden() then d(topLevel:GetName()) end end