Here is one I can't reproduce in smaller code. http://www.screencast.com/t/AJZjx1TjFT
You can see that when the enemies start off the canvas they end up leaving a smear behind. When they leave the canvas at the other end they also smear. I suspect it's something to do with the clipping code used in the game but I haven't been able to narrow it down (and this area I was a bit flaky on and I think Richard did the starting setup for). It's probably a case of clipping properly, but should this sort of behaviour be even possible to occur? p.s. thanks for the Camtasia tips - nice product.