Spells: Numb the Dead spell in ToFS

[Teku]

Hey there, anyone else have trouble with the necro/shadowknight spell Numb The Dead working in Tower of Frozen Shadow? I just got my 39 SK there and am on the second floor (library). The spell acts normal when i get a resist (mob runs at me in attack mode) But on successful casts it appears to have no effect. I didn't try it on first floor as those mobs were trivial at 39. And haven't gotten my next key to try it on 3rd.