I have just tested the new build, and the mouse cursor leaves the main monitor on my system (Geforce 5600 with 2 Monitors connected using nView-driver - not a dual-graphics card system), but this should be no problem at all - I just tested some other games, and it happens in all of them, I only never noticed it before because I usually switch off the second monitor while playing :-)
But therefore another problem arose: when I run the game from Projectman the mouse cursor becomes invisible - this did not happen in the previous build.
EDIT: I just tested it again: it shows me two devices, one opens the game on the second monitor -> there the cursor dissapears, and the other device opens it on the main monitor, -> everythings fine there
So it think it's not a real problem at all.