Tryndamere Cannot Be Interrupted While dashing with E

I was playing a game as vayne an hour ago and an enemy Tryndamere started to dive me under tower, i tried to condemn him and right as my bolt was about to hit him he E'ed and totally negated my knock back, i have also noticed this when an alistar tries to headbut him at the same moment he goes to E and alistar headbut goes right through him as if he was not even there. I am 100% sure this is a bug.