7D firing twice when shutter pressed half way, anyone else?

Thanks ARShutterbug, I am using single shooting mode and not continuous as some have suggested. Maybe I didn't have my finger completely covering the shutter button but a bit off to one side and that caused the shutter to fire twice.

Remembering back to each occasion I don't think I was completely set up to take the shot.

Since the second time this happened I have been careful on my finger placement but the last time was in moonlight and we all know that is supposed to make one act crazy