When running a guest with mouse set to "optimize for games", the mouse pointer intermittently jumps to near the top of the screen. It happens over and over but is seemingly random. It will go short periods without doing it and then when you least expect it, it jumps again. It happens enough to get very annoying. It happened in full screen as well as windowed. When I set Parallels to not optimize mouse for games, the problem stops. When I set it to auto optimize, it has so far not happened. I tested at the desktop and also with a full-screen game running. It happens with a Linux guest and also with a Windows 10 guest. It does not seem to happen on an OS X guest.