Title is self explanatory, it appears Blizzard forgot to flag H MGT as a heroic because:
a) People are completing heroic and not getting saved and are farming it repeatedly,
b) The loot that drops in heroic is not tradeable.
This most likely is not intended. Blizzard has a very inconsistent history when it comes to banning people for exploiting this kind of error. Personally I’m going to err on the side of caution and not do it more than once per character.
Good luck gamers.