Darius W bug

I am pretty sure that some of you have already noticed this at times, but it is about Darius and his W.

Whenever Darius does not get off his W right away (Vladimir pool, minion dies right before you AA it but still get the animation off, etc), he starts to stutter. This gets really annoying at times, since he just stands still for a good second, as if he is shocked and is just gasping at the fact that he did not get his W off.