Recently when moving items from my vault I started getting errors due to items listed as 0 Quantity which could not be moved. After some investigation (and filing a ticket in case I was missing items), I found I have two hundred items in my vault that are listed as "0 in your vault", at least a few of which I recognise from turning in at the Recycle Beast. I had to move them into a category so they won't disrupt searches and mass moves.

As a result I believe (but can't check, or even duplicate on purpose) that sometimes when recycling from the vault, the Recycle Beast is occasionally removing the full quantity of items but leaving the item code itself stuck in the vault.