Attack damage PVP bug? Or am I missing something?

I can't for the life of me figure out why in PVP I can use a weak skill like horizontal slash and reliably always do atleast some degree of damage. But if I use more powerful skills like Jump 2 or coup I always seem to do 0 damage? These skills should be doing 3-5 * the damage as horizontal slash, so if I'm damaging with that skill there is no reason I can think of that I should be doing 0 damage with stronger skills.

Is this a bug? A known bug? Or am I missing something?