This happens to me consistently in every fight, with every class.
I find it easiest to reproduce with casters and their Staff ability... if you wait until the instant the projectile leaves the caster and then mash the button, I can almost always get it to cast a second time (if I still have enough AP) instantly. When out of combat and using it on a door or chest, I can usually get 4-5 projectiles 'per cast'.
