Game Mechanics: Post-Vamp Plane of Hate Mini Boss Loot Table Broken?

[Khazzad Oakenshield]

Our guild has killed roughly 40 PoH mini-bosses that are supposed to now drop the Shattered Emerald of Corruption for the final step of Ranger Epic, but we've yet to see a one single drop. It looks like the chance for this to drop is around 10% - 30% depending on which mini-boss it is, so we should have seen at least one drop by now. This rate seems to be more than an unlucky dry-spell, so we are beginning to wonder if the loot tables are broken. Any assistance is greatly appreciated.