Blind support gem doesn't work?

I have a support gem that makes the supported skill to 100% blind enemies on hit.

I've put it into Killing Palm just to try it out on some mobs.
So when I hit a mob with it I see an icon appears on top of it, but it doesn't seem to do any effect? Like, that blinded enemy is still following me around and it can attack me no problem.

Any tips on how it should be properly used? Or is it a bug?