I had that same problem, but i would catch the toon running off, lets say he went running straight ahead, i would click on his window so i could get the wasd keys to work (since they are on do no pass) and simply press w once and he would stop running, same thing for turning, you just press the key for the direction that the toon is running or spinning and it will stop...as for the cause i dunno, but you can catch it in time, hopefully before it wipes you.