As long as you're certain that you lost the keys, that makes a difference. If you got pickpocketed, the thief could easily have followed you home (or wherever) to find out where to use the keys ...
(The German PO still has a special postage tarriff for "unpacked keys". That's mainly for hotels, though, so that when a guest accidentally takes keys along with a tag that states the hotel's name and city and calls them to know how to return it, they can answer "just drop it into the next post box".)