[GAMEPLAY] Poppy's Heroic Charge vs Vayne's Condemn

This happened to me twice in one hour the other day, simply because I played Vaynes back to back. So as Poppy I have a 100% stun on a Vayne, I go forward and cast my E on her and carry her all the way into the terrian that should stun her. Now normally when this interaction occurs we both just get pushed away from each other, however on these two occasions Vayne casts her E while shes being carried by Poppy and Somehow Poppy is stunned into the wall the Vayne should have been stunned in. Yesterday was the first time id actually had Poppy be stunned out of her charge (in this particular situation vs Vayne) and Vayne is** NOT STUNNED AT ALL!** Truly a win/win situation for Vayne.

I sent this into Riot Support originally and the only thing the guy said was to post here so there it is.

All I really want to know is why this works and is it working intentionally?