I can't get an image but if you complete a black armory for the first time after getting the quest you can claim infinite keys. I would click in the key to claim it but instead of bringing me out of the menu it would let me claim another one. I kept claiming them until my post was filled up. I don't know if this is deliberate but I may as well report it.
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Are you talking about the Black Armory Key Mold quest or something else? All the Black Armory Keys are claimed in-world, not in a menu, so what you're describing doesn't quite fit with a description of how to get the Keys. Can you elaborate or share a screenshot?