Originally Posted by Althor

My mistake. The internal cooldown on JoW procs is still 4 seconds, the proc rate still seems to be 100%. However the cooldown is linked to the debuff, not the player.

Which means that if multiple people are casting spells at the target the procs are shared between those people. So people who cast more spells in a given period have a higher chance to "steal" the proc. And the more people hitting it the less regen each person gets because they can miss out on procs.

(Saw this from 9 minutes from a combat log).