Completing this chain on Heroic with the epic chain in the quest list creates a situation where you cannot complete the heroic chain.
The solution for this when running epic and not being able to complete is to abandon the heroic quests, when that is done it is possible to collect the epic reward. When doing the heroic chain it is impossible to abandon the epic quests thus making it impossible to collect the chain end reward.
I have tested this with two toons - one with the heroic chain completed and the epic chain in the quest list and on another toon with the epic chain completed.
Epic chain completed - heroic quest can be abandoned to collect the Epic end reward.
Heroic chain completed - epic quests cannot be abandoned to collect the heroic end reward.
The solution seems to be to abandon the entire heroic progress, complete the epic chain and then go back and do heroic again.
Has anyone else had the same problem ? Anyone know a way to solve it without abandoning all of the progress ?