Sometimes when I buy an item from the store, it will buy as many items as it can. This ends up spending the total amount of resource that the items costs, usually draining that resource significantly. It will drop all of the items that were "purchased", but the weapons have a rarity of "None" and seem to be notably worse versions of the weapon. If I had to estimate, I'd say it happens anywhere from 10-20% of the time. This bug also affects my co-op partner