Impact Shockwave doesn't work on Bear Maul

I can't seem to get this to work. Does it work for anyone else?
I am clearly heavy stunning enemies, but there is no Aftershock.

Edit: I did some testing on my Warrior and put Impact Shockwave on the default attack, you can tell it works I guess by the circle that comes up under the monster when they get stunned immediately

However on the Bear, the weird part is, even without the Impact Shockwave support I can still see this circle appear. It's like Bear Form has built in Impact Shockwave that is not specified anywhere, and the support gem does nothing.