Vertical scrollbars are missing in Safari and Chrome

All right, so this is a weird problem, but I thought I'd toss it out there anyway and see what comes of it.

Nearly all of the time, vertical scrollbars are missing in both Safari and Chrome. I have then turned on in System Preferences, and they show up in every other program, including another Web browser (Firefox), but they do not show up in these two. I just have a solid gray bar down the edge of the screen, as seen here:

But it's not as though the vertical scrollbar can never appear at all; if I shrink the window horizontally enough to trigger the appearance of the horizontal scrollbar, then both scrollbars will appear, as seen here:

As I said, I do see the vertical scrollbar in other programs I've tried. What gives? Why Safari and Chrome, and (as far as I've seen) nothing else? And why is the appearance of the vertical scrollbar triggered only by the appearance of the horizontal scrollbar? It would certainly seem to be a Lion issue since it affects two different programs, but I can't entirely be sure of that because both of these are based on the same Webkit rendering engine.

Any ideas would be appreciated. If this is, indeed, a Lion or Webkit bug, I'd like to report it ... but to whom?