I have synergy set up with Windows 7 as the server and OS X as the client. Randomley today the mouse pointer would disappear and hide in the background on the OS X side if I did anything on the Windows side.
Not sure why it is doing this but here is what fixed it
-You can’t have more than one workspace open
-The dock can’t be on the side where you are moving your mouse over from your server
-After doing both of these restart the synergy program on both the server and the client.