Got to Crystal the other day as WHM but this is the first I'm hearing of such a bug. Wouldn't be surprised if I did it on accident like other people are saying. If cancelling the cast is all you need to do, then banning for it would hit a TON of innocent bystanders, seeing as cancelling casts is something you do all the time in PvP either to move, guard, recuperate, get pushed or interrupted by an enemy etc...