Windows 7, FTW! I keep my taskbar on my second screen, btw.
That being said, I see no point in people posting here that they like it the way it is here. It's an OPTION that is being asked for. If you don't like it, don't use it in game. Understand that others may like, for example, to scroll map by moving to the edge of the window and they can't do that ATM when they have multiple monitors. Why would they be forced to play the way YOU like?
Positive feedback is just as important as negative feedback. Without those of us saying it's useful, the devs might decide to reverse the behavior, rather than make an option. So that would please the OP, but would annoy those of us who like it the way it is.
More to the point, however, the OP doesn't say squat about making an option. The OP explicitly says that allowing the mouse to move to the 2nd monitor is a bug.