title: Using ng-model on prototype properties, cannot edit input field
body: <p>Plunker - <a href="http://plnkr.co/edit/l9ZzBilMaf3eJgXDNcaK" rel="nofollow">http://plnkr.co/edit/l9ZzBilMaf3eJgXDNcaK</a></p>
  
  <p>I have a funny feeling this is related to the prototypical model and I should be doing some clever binding but I can't figure it out. </p>
  
  <p>I'm trying to improve existing code and I'm experimenting with prototypical constructors with angularjs factories. As you can see it all seems to work great except that I cannot edit an input field which has been bound to a property of one of my created objects.</p>
  
  <p>Can anyone shed some light on this? </p>