I have experienced this problem in both 12.04 and 12.10.
https://bugs.launchpad.net/ubuntu/+source/compiz/+bug/964270 (12.04) https://bugs.launchpad.net/ubuntu/+source/compiz/+bug/1063617 (12.10 and later)
I'm wondering if someone could confirm that this bug is fixed in 13.04.
If it's not, I probably won't upgrade. That's my only annoyance with 12.10 now.