The list of recent items shown to the user in an autocomplete is basically never cleared unless they clear it themselves. This can be dangerous in cases where a stored entity was merged or removed: the user will still be allowed to select the entity, but the edit form submission will almost undoubtedly hit an internal server error due to the ID being nonexistent.

Recent example: https://sentry.metabrainz.org/metabrainz/musicbrainz-server/issues/750/