Page up/down has surprising behaviour if the UI focus is in the thumbnail pane (focus is not clearly indicated)
Submitted by Vivek Dasmohapatra
If the focus was last delivered to the document-page pane, Page-Up/Page-Down behave as expected: The display moves to the next or previous page.
If the focus was last delivered to the thumbnail pane, the view instead jumps by one screen's worth of thumbnails, whatever that might be.
This would be Ok, except there's every little UI indication that the focus is in one pane or the other: If the focus is in the thumbnail pane and the "most current" thumbnail is in view, them it has a very faint dotted line around the thumbnail.
Other than that, clicking or otherwise transferring the focus between the two panes has no noticeable UI feedback, which can lead to very puzzling behaviour.
[ Primary testing on 3.14.x but I had someone confirm with 3.22.x ]