Because Alf is in the challenge, I obtained a second gold aegis crystal for the demonblood quest.
I placed one in my vault and kept the second on Alf.
I completed the quest.
I returned to the vault to exchange the demonblood crystal with the duplicated gold aegis crystal.
The quest seems to have converted both crystals into one demonblood. The one in my vault and the one on Alf's person have both been removed. In exchange, there is one demonblood crystal.
This looks like a bug in the code recognizing distinctions between items in the vault and on the player when completing the specific demonblood quest.