Ashe Ult Passing Through a Champ

After a teamfight, my team's Ashe shot her ult at a Viktor. There was no doubt that the arrow would have hit because it was perfectly lined up towards the enemy Viktor. Instead the arrow passed through him and even the Viktor admitted that it was bugged and the arrow should have hit.

Game Mode: 5v5 Normal, Summoner's Rift, Blind Pick Date of Game: June 15, 2015 Champion Pick: Ryze