Vel'koz W Bug

If you cast vel'koz w right before he dies, it will start the animation but will then stop without doing anything else. I've even had it do the first round of damage but then dissapear because i died and it didn't do the second burst of damage. Wanting to know why this happens since his w has no cast time. If you cast it right before you die and you start to see it, it shouldn't just stop.