If they introduced re-locking, I could see vanishing keys being an issue. No idea if they have a plan for that.
Another option is, again, have everything automatically go to the keyring - keys never touch your inventory. And then be able to filter the keyring to see which keys haven't been used yet. So you don't lose them, but you can quickly identify any keys you have sitting around that you haven't matched up with a lock yet. That should handle all of the situations that have been mentioned so far.
