title: CollectionViewSource CurrentChanged not triggering
body: <p>I wonder if I am doing something wrong? My CurrentChanged does not seem to trigger. It only triggers on application start</p>
  
  <pre><code>ListItems = new ObservableCollection&lt;string&gt;();
  ListItems.Add("hello");
  ListItems.Add("world");
  ListItems.Add("foo");
  ListItems.Add("bar");
  ListItems.Add("baz");
  viewSource = CollectionViewSource.GetDefaultView(ListItems);
  viewSource.CurrentChanged += (o, e) =&gt;
  {
      MessageBox.Show((string)viewSource.CurrentItem);
  };
  </code></pre>