Summary: fieldsets don't repaint completely when their size changes, so parts of their border are either missing or left behind. To reproduce: open the testcase in Safari. Click each Test button once. Expected: the bottom border to be painted correctly after resize. Actual: in the top case (shrinking), a segment is missing on each side of the bottom border; in the bottom case (growing), a segment from each side of the bottom border remains behind.
Created attachment 5377 [details] testcase
Actually, this is a problem with borders in general, a DIV with solid border works just as well in the testcase.
Created attachment 5380 [details] Repaint moving border Like with bug 5699, an automatic test is currently impossible.
Comment on attachment 5380 [details] Repaint moving border What about borderLeft/Top?
(In reply to comment #4) > What about borderLeft/Top? The left/top borders don't move so there's no need to repaint them. You're in this case: // We didn't move, but we did change size. Invalidate the delta, which will consist of possibly // two rectangles (but typically only one). You only need to extend this to include the area that was/will be occupied by the border that moves.
Comment on attachment 5380 [details] Repaint moving border r=me
Removing keyword(s) since bug is fixed.
Removing Regression keyword from bugs already fixed.