OnApplicationPause not called on Windows Store app

I have an OnApplicationPause function in one of my scripts:

 public bool isPaused;

 void OnApplicationPause( bool pause )
 {
     isPaused = pause;
 }

When I build/run for Windows Store on my Surface (v1), I find that the function is called when the app launches, but it is NOT called when I send the app to the background by hitting the Windows button on the Surface.

I have reproduced the problem in 3 separate Unity projects, including the Stealth sample. I'm using Unity 4.5.1.

Does OnApplicationPause work on Windows Store Apps?