[GAMEPLAY] Yasuo can dash out of Rek'sai's knockup

Riot, In a recent game I was playing Rek'sai and an enemy was playing Yasuo, he was running from our team and i tunneled to him and knocked him up. During the knockup he dashed to my allied minions and got away. His dash skill says nothing about getting him out of knockups so I'm not sure why this happened. I didn't even get to get one melee attack off with Rek'sai after knocking him up, no other creatures were near us for me to mistakenly knockup either.

To reproduce this bug, have Rek'sai knock up a Yasuo and have him dash right as he gets knocked up.

Thanks Nick111567