[GAMEPLAY] Duskblade of Draktharr not always triggering when used by Kha'Zix

When Kha'Zix auto attacks a champion with Duskblade of Draktharr's passive trigger available, it does not always apply the debuff. In a game I just played, the item did not trigger on champions I auto attacked in multiple instances throughout the game. The bug may be based on Kha'Zix's passive, where maybe the game counts the passive proc as a spell cast and doesn't apply Duskblade? I do not have more information but I will play more games on Kha and update this post if I can find any more clear information.