Alright, thanks for all the feedback. Given that the boxes go away when logged out, and that Denver is on -radeon whereas Andreas is -intel, it is likely sounding not to be a driver issue. It is probably compiz doing something wrong.
I see there are similar bugs against compiz, #940603 and #753606, but the symptoms differ, so not setting as dupe. (940603 is also against chromium, so may be pertinent) ** Package changed: mesa (Ubuntu) => compiz (Ubuntu) ** Changed in: compiz (Ubuntu) Status: Incomplete => New -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to mesa in Ubuntu. https://bugs.launchpad.net/bugs/935630 Title: White rectangular To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/compiz/+bug/935630/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp