title: Selecting an option in ngOptions doesn't update the model
body: <p>I have a slightly complex object structure:</p>
  
  <pre><code>$scope.items = 
  [
   {
     name: 'something',
     complexObject:
       {
          number: 1,
          id: 12345
       }
   },
    …more of those
  ]
  $scope.selectedItem = $scope.items[0];
  </code></pre>
  
  <p>Now I want to create a dropdown box like this:</p>
  
  <pre><code>&lt;select 
     ng-options="item as item.complexObject.number for item in items track by items.complexObject.id" 
     ng-model="selectedItem"&gt;
  </code></pre>
  
  <p>When I updated <code>selectedItem</code> with another item, the according number is displayed in the dropdown box. But when I select an item from the box the selectedItem is not updated. What I noticed though is, that all options I pick get the 'selected' tag in the DOM.</p>
  
  <p>Any advice?</p>