Move the mouse over the example page. Notice the rendering bugs (using r25145 here): Parts of the page are not redrawn properly. Here's another URL with the same problems: http://www.walterzorn.com/tooltip/tooltip_e.htm
Confirmed with r25153. This is a regression from Safari 3.0.3 Beta.
Created attachment 16036 [details] Screenshot
Created attachment 16039 [details] Reduction
Created attachment 16042 [details] Cache layers' repaint rects when they turn visible Includes repaint test
Comment on attachment 16042 [details] Cache layers' repaint rects when they turn visible r=me
Committed revision 25168.
<rdar://problem/5435092>