Lubuntu 14.04
Nvidia 352.63
There seems to be a bug where the cursor of a guest (in this case Windows XP) will periodically get stuck in random places on the desktop against an invisible box if you disable mouse integration (so the cursor is locked to the guest). With alot of thrasing you can eventually move the cursor around the invisible box but its quite annoying. Imagine if you track horizontally across your monitor and your cursor hits a "wall" 2/3's of the way to the other side and only then tracks vertically from there on until a certain point where you can finally go around it. It's literally like random invisible boxes on the desktop. That's the type of symptom i'm seeing.
This seems to be related to multi monitor setups. I've searched far and wide and the only other post I've seen on the issue said to disable your other monitors, but thats unacceptable. For anyone else looking, I'm presenting my own workaround:
You will have to arrange your monitor setups so they aren't directly snapped together:
BAD
GOOD
With a bit more precision you can adjust the actual values listed in the Position coordinates by a couple values to fix it as well.
key words:
cursor stuck invisible multimonitor mouse