Trist zero damage Autoattacks

Game played on 24/02/2017 as Trist (defeat) vs Kalista, if you can look at replays. In the last fight of the game, when casting W on Kalista, the next 3 Autoattacks applied W stacks but did zero damage. She had no shields on her. She also continues to attack during Malz ult in that fight, but that seems to be a known bug? looked like her AA animation started after the ult