*ahem*
sorry for making it look like I'm bring an out of date thread back to life, but you may want to check dead systems to. I've noticed if you start pummeling a ship, there's a chance you will actually see attack nano trying to destroy a system that's already dead...
I'm thinking it's because the system got targetted, but then was destroyed by an explosion, rather then attack nano...
at any rate, the only times I've seen it happen is when the ship was... doomed, to say the least

(this was also on demo, haven't seen it happen to anothe rplayer yet)