[Gameplay] Vayne Condem (E) Getting block by Lee Sin

I am playing Vayne vs a Lee Sin. So what is going on is that Lee some how can block my Condem (E). I after watching replay i can see that he is taking dmg from it. But that it does no knock him back. He block while he was basic attacking and using his Tempest/ Cripple (E). It happen to me two times in one game and i got killed both times cause of it. Watch Replay for example of it.