First I'd like to say I dont seem to have nearly as many issues as other players. Im really enjoying the game and I've been a supported since alpha :).

Title says it all, I built a character and even though I have 15% chance to apply stun on physical damage, enemies are never stunned.

I've been primarily using basic attacks with a pistol/shotgun and using the Wailing Arrows skil. Neither of which seem to apply the stun. Occasionally I use Wings of... (forgot rest of name, the jump skill for melee weapons) and that doesn't stun either, the stun modifier for the shout skill works fine.