Well I can't help much here but the bypass option allows the mouse to revert to the server if it should get stuck on a client.

Modifier keys effect how its broadcast, ie if client A thinks shift is down, it looks for shift combo's. Whether shift is down and whether the client thinks shift is down is 2 different things.

The mouse driver is not for WoW and... it generates more questions than it is used i expect.

Theres other KM's like multibox and also input director (which i never tried) too. they r free.