Azir ultimate bug?

Hello guys, I recently played a game as Nasus in top lane and I faced Azir.

The bug occured when Azir ulted me into terrain near my tower, I could not move in any way and was perma knocked up. I was able to move after the ultimate ran out, but this experiance was a bit butthurting :/

I was wondering if this happens a lot, or if I just got really unlucky.

(PS. I thought this was already fixed?)