I have rechecked vs latest beta build of 2.82 and find the issue as reported is resolved.

Just touching this as it it still exists. Seems possibly status is wrong and should have be changed to "Confirmed" when it was assigned by Bill

Attached requested simple blend file. Scene has 2 animated cameras, with camera change at frame 25.

Clement, as you noted in T62961 (which I agree is a duplicate description of this from a different point of view) tagging the viewport for redraw seem to be the root symptom. The root cause questions to still resolve seem to be:

Just one other detail. I noted that closing and reloading this .blend file changed the behavior to redraw on mouse movement, so obviously there is some state var that can get mangled as well but clears up on reload. Video shows redraw on mouse hover, but now I am seeing it on mouse move in same regions.

Suggestion for a possible solution to this: Nesting of 2 containers, with no mouse position testing on the outer container.

Understood. Will submit a suggestion on this.

Retested on V2.80 18e5540a48b6 Build 06-Mar-19 00:18, Issue still exists

Checked on build 2019-03-01 10:14, and behavior is the same. It only takes seconds to reproduce from default scene. Screen shots of splash screen, viewport view through camera and render attached.