Poppy failing to stun Fiora, possibly on any movement!

I played against a Fiora, and four different times while fighting her as Poppy my e failed to stun. Each time it should have been an obvious stun, we were very close to a wall. But what I noticed was that each time it happened it coincided with her using her dash. Either she was being knocked up by my w or she was beginning a dash, and the stun would fail. I hope this is not intentional. And it should be fixed, made it incredibly hard to fight her and led to much frustration. Thank you Riot!