This sounds like bug 57344; it was a race condition most people were not able to trigger with metacity versions prior to 2.15.34, but which became easier to trigger with that version. Differences in hardward definitely affect the ability to reproduce race conditions such as these, and you may have just been one of the unlucky ones. There's a patch in http://bugzilla.gnome.org/show_bug.cgi?id=354422 that should fix this for you, if I'm right about my guess.
-- window selection problems https://launchpad.net/bugs/45611 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
