Lucian Ultimate+E bug [GAMEPLAY]

To begin with, I was testing the new Buff on practice tool and suddenly I came across with a Ultimate (The Culling) + E (Relentless Pursuit) bug. Basically when I use my ultimate and then my E It breaks the animation and I can use all my abilities and AA. This issue doesn't happen every single time, or maybe I'm doing it wrong, but the way I think it is, is using ultimate and then E. I've upload a video on youtube so you can see how it works.

Link of the video : https://www.youtube.com/watch?v=ixBLqI83d-k&feature=youtu.be