Let's imagine a library agreement like this one: "Bob may possess the book on the condition that he returns it on Friday. Furthermore, Bob agrees that should he make a copy of the book, he hereby transfers ownership of such copies to Alice."

Now if he sends a copy to Carol, he's sending Alice's property to Carol. The ownership of the new copy was permanently established due to Bob's binding contract.

Bob could argue that he "broke" the contract and therefore does not recognise that the copy is Alice's property. But if merely saying so was sufficient to break a contract, we wouldn't have contracts.