Snow Down Your Shirt - A dud?

I've used this new Wintersday hex quite a lot so far in Snowball fights, and it seems to be bugged. It may knock down once on occasion, (Which may be an ally using Hidden Rock) but other than that I get no further knockdowns no matter how much damage I inflict on my target. Is the skill bugged and is not working, or does it only activate once then dissapear, and the desription is saying the wrong thing?

I'm not logged in atm but isn't it only interuppts and not knockdown. Yes KD when you hit an interupted skill, but that's all it does.

it only interrupts, it doesnt KD the target. That skill and hidden rock seem to be alittle bugged though, because with both of those skills active on me, ive been able to get a few skills off without getting interrupted by either skill even though the description says I'm supposed to sometimes. However, for the most part ive seen snow in shirt work correctly.