This is a hard one to explain, so I'll try my best. When a client is running a program that requires some special behaviour on the mouse, synergy will not take this into account, breaking some apps functionality. Example 1. Happens mostly on games: Most games need to be able to lock the position of the mouse to the center of the screen, to allow "infinite" movement in any direction. This won't work with synergy, since it bypasses the locking mechanism, restricting the in-game