Switched Magical Items

As Jon slept, a shadowy figure snuck into his room. He traveled along with his back flat to the walls. The last thing he wanted to do was wake Jon. The mysterious figure ever so carefully snatched the wishing stone and put something else in its place. But the thing he put in the stone's place was not a stone, but rather a different (but still magical) item. And then he left the room, as stealthily as he had entered it.