title: Calling Backbone.Model.Save converts child-Backbone.Model to object?
body: <p>I'm creating a Backbone Model which has a child Backbone Model inside of it:</p>
  
  <pre><code>console.log("inside add item, video:", video instanceof Backbone.Model);
  
  var playlistItem = new PlaylistItem({
      video: video,
      title: video.get('title')
  });
  </code></pre>
  
  <p>afterwards, I save it:</p>
  
  <pre><code>playlistItem.save({}, {
      success: function() {
          console.log("Successfully saved.");
          playlistItem.get('video').get('title');
      }
  });
  </code></pre>
  
  <p>In this example, I encounter an error -- video is not an instanceof Backbone.Model after calling save. Why?</p>