Observable only on Vista, since that's the only style that paints scrollbars diffrently for hovered and sunken states, but easily reproducable with a patch to the plastique style.
1. First time hover paints hover-state, but any hover after that does not.
2. Click on a scollbar paints sunken state, but moving the mouse away from the scrollbar while still pressing down goes back to painting hovered state, instead of keeping the sunken state.
Fixed in http://code.staikos.net/cgi-bin/gitweb.cgi?p=webkit;a=shortlog;h=torarne/scrollbar-paint-fix and integrated into the qtwebkit branch.
Adding patch for review
Created attachment 20819 [details]
Looks good to me, but there's a break; missing after the call to d->leaveEvent() in qwebpage.cpp :)
Created attachment 20862 [details]
Comment on attachment 20862 [details]
Landed in r32613