Some siege units glitching out.

Is it just me, or has anyone else noticed that some siege weapons look like they're attacking, but don't do any damage sometimes?

So far I've seen this with Petards and Bombard Cannons. I remember trying to bust through my opponent's gate with 2 Petards on Arena to find that only one of them did any actual damage.

Similar story with Bombard Cannons. Their cannonballs make contact with the buildings I'm blowing up, but no damage registers sometimes, especially the first shot.

What the hell is going on?