title: Backbone Collection not unique?
body: <p>I've got a simple setup going for the beginnings of an app in Backbone.js<br>
  The code is in <a href="https://gist.github.com/3935931" rel="nofollow">this gist</a>.<br>
  It is pretty straightforward.  A <code>Coin</code> model and collection, a <code>Player</code> model and collection.  Each Player has a collection of Coins.  I manually add the type of Coins a player should be getting.  </p>
  
  <p>At the end of <code>initialize</code>, each of the Players <code>Coins</code> collection has 32 items in it and <code>Coins.player_id</code> is set to 4 in all 4 Players.  </p>
  
  <p>What am I missing?</p>