Sett vs Fiora: The Stunning

Having played a few games as Sett vs Fiora, I noticed something about the interactions of his E and her Parry. When I used his E AFTER her Parry animation completed, both myself and the Fiora were both stunned. From my understanding of Fiora's Parry, she shouldn't be stunned if she successfully Parries hard CC, but in the case with using Sett both champions end up stunned. That issue as well, I'm sure to only use it after her Parry animation completes, so I feel that the issue is more with Fiora than Sett but I don't know. Has this happened with anyone else?

Edit: Well, it's not a matter of auto attack cancelling and i just don't notice. I checked replay to confirm and Sett's not stunned (there's no indicator even though there is one over Fiora). Can't move, can't attack, can't use abilities.