[{quoted}](name=Deep Terror Nami,realm=NA,application-id=LqLKtMpN,discussion-id=L9EwwfWv,comment-id=0000,timestamp=2017-01-22T10:35:00.503+0000)
It's pretty unfortunate, but it's simply because he's untargetable (you have to be careful about positioning when your ally can do that frequently). The ball has to go somewhere, but it can't go to him so it pops back to you.
I recommend posting on Gameplay to discuss this interaction, as it definitely has some merit. I personally would prefer that it drops to the ground where it's at, so that it would tend to be near where you wanted it.
But what makes him untargetable though? all i can see is that he is knocked up by thresh e when i e him, but that shouldnt make him untargetable(unless it does and im mistaken). He has already used his w at the beginning of that clip, onto the vayne, a few seconds before i e him so that untargetable time wouldnt affect it. i mean maybe he has 40% cdr and does a short range w right when i e him but i couldnt see it. Im going into this a bit deep but its interesting and id like to go into this field in a few years.