One work around that you can use if your going to stay with Synergy is the "Scroll Lock" key. Move your mouse to the screen you want to mouse look with. Press the "scroll lock" key and this will anchor the mouse to that screen so you can mouse look with that character. Hit "Scroll lock" again and you can move your mouse to the other screens again. There is no permanent fix I am aware of. On a side note, have your ever looked at the character that spins when this happens with one of your other characters....hilarious. =P