This is an exploit I found last week with my guild in the 25 man version of Hallion in the Ruby Sanctum, we were surprised to say the least.
What we did was have the instance set to heroic as we cleared all the trash and first 2 mini-bosses, after you have killed the last mini boss you must switch the difficulty of the instance from heroic to normal the moment you drop combat. Hallions RP will bug out, and it will look as if he appears twice. Engage and kill Hallion as normal, and he will drop the heroic (284 ilvl) loot. We have only had this happen once, by accident and have no experience attempting this on 10 man.
We did not attempt to bug the encounter again this week, but I thought I would make an account and share.. as for some reason my old account has no posting privileges.