Actually, it also happens in MP, it is just HELLISHLY rare. Sometimes you block and the weapon goes right through the opponent's head for massive damage.
Red style can do weird block attacks on rare occassions, blocking into a killer lower right to upper left diagonal if you hold the attack button. Staff does something similar. If they go off you've pretty much won due to how deadly they are. But I've never seen any of the other styles do it.