Found a doozy of a bug in Revendreth tonight. It involves the buff from an Overflowing Chalice and the death knight ability Breath of Sindragosa. Normally, BoS costs 16 runic power per second of use. However, if you use the skill while Overflowing Chalice is active, it remains permanently in use, even when Chalice expires. The only way it runs out following this is if natural out of combat decay of runic power drops you below 16 RP, or if skills like Frost Strike drop you too low.
Already reported it using the bug report feature from in game. Also going to tag the WoW Twitter account as I feel this is a big deal and can potentially make mobs in the zone trivial with very little effort so long as a death knight manages to keep their runic power above 16 once they manage to activate the bug.