Please see the attached screenshot which I took of emacs while
composing this bug report inside it.

Periodically Emacs gets confused in some mysterious way and stops
rendering its scrollbars properly or resizing properly. See the right
side of the screenshot for the messed-up scrollbars and the bottom of
the screenshot for what happened when I attempted to make the window
bigger vertically. The compositor thinks the Emacs window has been
resized, but Emacs is still rendering at the old size.

I haven't seen this kind of behavior in any other apps.

The only way I've found to recover is to quit and restart Emacs.