Vi bug?

https://www.youtube.com/watch?v=7uvIKXmKfMc&feature=youtu.be

I was playing VI and i think i may have counter a game breaking bug especially during the late game. The ult seen to not connect or finish doing the animation and putting the Ult on cooldown. Note that the enemy team does not have QSS or any kind of way to get rid off vi ult. Vi ult cannot be stop during the channel so is this a bug or is there a change that i miss? Watch carefully on the ezreal as i ult him during the fight.