I know this is my first post and all, but i can confirm this sorta.
We were doing heroic AN. We had a pretty pimp group we usually run the place in 12 minutes anyway, one of the DKs didnt feel liek waiting for him to kill the adds so he just went after the boss before he made his way up from killing the adds. So anyway way we're all fighting the boss and the little adds that hes supposed to kill keep spawning and spawning lol well little did we know those little adds actually healed him. We ended up wiping becuase the healer went oom after like 9 minutes of him getting healed from 95% to 100%. On our way back and ready for round 2 after we learned our lesson we lkilled the 3 elite dudes to trigger the boss. When he came up the tank pulled him with his gun and the boss just died in 1-hit.
I'm hoping this will help you guys narrow it down a little to exactly what causes it. I personally think it has something to do with the little adds.