title: ng-model isn't updating when I change a select option
body: <p>I have a select box with some <code>ng-options</code>, but it's not updating the <code>ng-model</code> when I select an option. I have a fiddle up at <a href="http://jsfiddle.net/32tntojs/" rel="nofollow">http://jsfiddle.net/32tntojs/</a> to view the source.</p>
  
  <p>My HTML is</p>
  
  <pre><code>&lt;div ng-controller="MyCtrl"&gt;
  PARENTID: {{ parent_id }}
  &lt;select  ng-model="parent_id" ng-options="project.id as project.groupingName for project in projects track by $index"&gt;&lt;/select&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>and when I select something, the <code>parent_id</code> doesn't update. What am I doing wrong?</p>