I did another post about this on estelle but now that I'm finding that it happens to other strikers as well I think it might be a game wide bug.(haven't tested all of them so not sure yet)
Here's exemples for estelle and drek'ar:
#Using an ability during another ability's animation cause visual / audio bugs
remote notch
Basically the visual bug is that some part of the ability's animation shows up in the direction you're walking in instead of the direction you're aiming at.
Sometimes you also get the start of an animation and/or an audio queue for the ability you're using but it doesn't fully go through.
All of this only seems the happen with ability's that can be activated during another ability's animation but it isn't meant to.