Dunno if its a bug or..
While i'm kiting zombies, if i do it fast - i hear the shotgun sound, i loose 1 ammo but i don't see the animation of the shot, therefore no damage done.

it happens for the sniper too... double shots because he just shot at a zombie and you gave him a command.... the first shot doesn't do anything, but you still lose ammo...

That's because there is no event in the wc3 triggers to check when a unit takes damage, only when they starts the attack. And if that attack is stopped the trigger will still run and take away your ammo etc.

lol it's an ammo stealing Trigger

Actually... I meant to bring this up earlier... Sniper losses ammo MUCH faster than that.. I have sat and watchied his ammo drop from 15-8 in 2 seconds without him being givin a single command. The thing is... if he fires at an enemy who is about to die already, he reloads and fires again instantly. so if he continues to attack targets that are dying.. you will continue to lose ammo much faster than normal. and his reload speed has no effect on how quickly he fires lol

lool ammo whore

I cannot remove this bug completely, but I have changed the units' animation damage so that it will happen much less.
I haven't tested it yet, but the Assaultman should benefit the most from it.