I have the same problem. It has been solved by changing the control theme as it has been suggested by David Rogers.
Maybe the problem is related to drawing boxes with rounded corners, since all the themes with slow down reported by Rogers have boxes with rounded corners. Thanks, Sergio. -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org