Fiora bug with polymorph (maybe)

I played Lulu into Fiora recently and when I polymorphed her right as she lunged, she still dealt the damage and the damage associated with her passive when hitting the vital, which she still targeted and attacked when fully polymorphed. She was fully polymorphed when she got finished the lunge part. IDK if this is intended or what, but it seemed strange that she still damaged me since it is a 2 part ability. I can understand a timing issue where the polymorph projectile didn't reach her in time. But in this case she was hit before the lunge half was finished. Since the attack is melee and not a projectile, it just seemed odd.