Fortunately, Jon had a good head on him and he saw a way to get around the rules of this "fake" stone.
"I wish that my grandfather who died was actually my grandmother who died." The stone glowed, because something female was included in his wish. In this case, the word grandmother.
"Now, I wish that I had the stone that I got from my grandmother." The stone glowed again and suddenly the normal wishing stone appeared in his hand.
Somewhere else, in some other darkly realm, The Keeper sat on his throne, gloating over the fact that he had finally acquired the most desired stone of all!
And then it was gone.
