I installed gtk2-engines 2.8.0-0ubuntu1, and after logging out and then in again, the problem is resolved! No more ugly frames where they don't belong.
Perhaps this should be marked as fixed once the package hits the repos? -- Ugly frames show in widgets with some gtk2 themes https://launchpad.net/bugs/58659 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
