I read the following claim in [this book][1] (after Fig. 4.3). Angular momentum changing in multiples of $\hbar$ is compelling only for a *complete* system. Division of angular momentum change between the parts of a coupled system doesn't have to be in integral units of $\hbar$.    
Any clarification or examples?


  [1]: http://books.google.de/books/about/Principles_of_Magnetic_Resonance.html?hl=de&id=zgnrRkaIhFoC