I run dual monitors. This from experience. If you run your game in full screen mode, you'll only be able to get out of that using alt-tab or windows key etc. If you run the game in windowed mode and open it all the way up, you'll still be able to swap monitors. It a matter of how windows sees things. In full screen, you are using the OpenGL drivers etc, so that's an actual application, which had its own mouse pointer in game. In windowed mode, you are still in Windows, so the aux screen is nothing more than an extension of the primary and uses the windows mouse pointer.