I have the January Avatar patreon version that reworked the inventory system, so I guess that's what made keys sellable, so it might still be an unavoidable bug in the Steam version, the only solution there would then probably be to start a new game and be very careful to never loot more than one key, but even then I'm not sure it would work 100%.How you can sell quest items? I have two keys, marked as quest items, I tried all merchants and nothing.