not a really bad one, but still:
on a new set in arrangement view, create about 6 return tracks, display them, and unfold a couple of them.
the scrolling bar gets smaller.
if you hide the return tracks, it stays small.
if you go to session and back to arrangement, it gets back to normal size.
what's stranger is that if you open the I/O section while the return tracks are shown, the scrolling bar will shrink (though the I/O display doesn't affect vertical size).
just click randomly on "R", "I/O" and the Tab key, the size of the scrolling bar is just inpredictable.