title: ComboBox Items not refresed after reseting DataSource
body: <p>I have a couple of ComboBoxes on a Win Form that I always set list to the DataSource like this:</p>
  
  <pre><code>aComboBox.DataSource = someList;
  foreach(Object obj in aComboBox.Items) {
    // do something
  }
  </code></pre>
  
  <p>This works perfectly fine for me, however, I have some trouble when trying to reset the data like this:</p>
  
  <pre><code>aComboBox.DataSource = null;
  aComboBox.DataSource = someOtherList;
  foreach(Object obj in aComboBox.Items) {
    // do something else
  }
  </code></pre>
  
  <p>The DataSource is reset successfully, but that does not trigger to reset the Items. I tried to call <code>aComboBox.Items.Clear()</code> to clean up the Items, no resetting happened.</p>
  
  <p>Have I missed something?</p>