Black Core Corpus Malachus Game Ending Bug

When you complete the Corpus Malachus quest and hand in all three pieces to Piety, you must enter the room immediately or your character is stuck.

My issue is piety is gone when i zone in, it doesn't let me enter and killing the bosses again doesn't drop the pieces.

When i zone out, high gate it prompts me to kill malachai, when i zone in it does the same thing only when i click on the room to enter does it say to get all three pieces, but they dont drop / piety is gone.

http://imgur.com/a/JP5kD

The text on the screen when you click the opening tells you what you need to do. There can be no living guardians in the instance you try to enter the black core. Kill them again and use the same instance to enter the core. New instances reset all the guardians back to living.

I get that this is likely done to make it harder to farm Malachai but it really screws over first time/casual players. Please at least make it clear in the game that there is no point in killing the three guardians unless you also plan to enter the black core in that same play session.