I also frequently experience what sounds like the same bug (clicks going "right through" a fullscreen Iceweasel or fullscreen game and being received by whatever is underneath; keyboard events are delivered correctly). For me, though, it happens with fullscreen applications on my single screen -- no multi-monitor setup required.
-- Nathaniel J. Smith Postdoctoral researcher - Informatics - University of Edinburgh http://vorpus.org -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org