Comment 9 for bug 712101

Oh, I know what this is! In Patrick's screenshot, Ubiquity is the correct size. This problem comes from the fact that scrollbars take up space, inviting more scrollbars. (From which emerges an evil chicken & egg conundrum).

If a window starts off too small, the vertical scroll bar appears. Because the vertical scroll bar takes up space, the horizontal scroll bar appears. Now the actual content area is a lot smaller, so even if you bring the window up to the correct size the scrollbars will be present. For the scrollbars to go away, you need to make the window bigger than it needed to be at first, then you can shrink it again.
I bump into it a lot doing web design :)

With Ubuntu, we're going to have those fancy new overlay scrollbars that don't take up space, so I bet this problem will magically go away there, but we'll still have this occur for other distributions that use Ubiquity.

This could still be a Ubiquity thing, but now I understand the problem better I am reopening for the slideshow. I can't think of any case where content would extend past the bottom of the page (and overflow:hidden in the slideshow container should deal with that), but I could be missing something…