1. Go to http://fremdsprachenwerkstatt.ch/module/8/1/6 2. First click on the second "Antwort" link. Some text will appear. 3. Now click on the first "Antwort" link. Again, some text will appear. Notice that the list bullet of the second list item didn't move. This is a redrawing error, because it appears at the correct position when selecting the text or resizing the window. Happens using revision 19879. Doesn't happen with shipping Safari.
Created attachment 13400 [details] screenshot of the problem
Regressed between r18756 and r18765. Likely candidates in that range are <http://trac.webkit.org/projects/webkit/changeset/18758> and <http://trac.webkit.org/projects/webkit/changeset/18762>.
Created attachment 13404 [details] Reduction
The root cause of this bug is that list mark repainting is still not perfect (duh). Specifically, RenderListItem::positionListMarker() should adjust the horizontal overflows of all blocks between the marker and the list item, not just the list item. You can see the repaint problem in a static case too if you just make the body wider in the reduction and scroll to the right and then slowly to the left.
Created attachment 13409 [details] Add marker overflow to all ancestor blocks up to the list item
Comment on attachment 13409 [details] Add marker overflow to all ancestor blocks up to the list item r=me
Landed in r19899.