Power Knock-Back damage is way off

Describe the problem. Be as specific as possible!:

Power Knock-Back's damage is way off. It took over 15000 damage with it in order to kill a zombie mushroom. No, it wasn't lag, since it killed a stirge in the same set of swings. I tried using my other skills to make sure that it wasn't just all the client-side rolls not in sync with the server, but the others ones all seemed OK.

Kind of hard to show in pics, but...

 Images of problem

In this one, you can see the mushroom clearly being knocked back, yet it survives a 1.8k hit.


The 3274 on the top left bat is very fresh in the picture. The exp gain is almost completely faded already, so it's from a previous bat and the one with the 3.2k didn't die. I was trying to show that I wasn't lagging