title: WinForms ComboBox DropDown and Autocomplete window both appear
body: <p>I've got a <code>ComboBox</code> on a winforms app with this code:</p>
  
  <pre><code>comboBox1.AutoCompleteMode = AutoCompleteMode.SuggestAppend;
  comboBox1.AutoCompleteSource = AutoCompleteSource.ListItems;
  
  DataTable t = new DataTable();
  t.Columns.Add("ID", typeof(int));
  t.Columns.Add("Display", typeof(string));
  
  for (int i = 1; i &lt; 2000; i++)
  {
      t.Rows.Add(i, i.ToString("N0"));
  }
  
  comboBox1.DataSource = t;
  comboBox1.ValueMember = "ID";
  comboBox1.DisplayMember = "Display";
  </code></pre>
  
  <p>I then follow these steps when the window opens:</p>
  
  <ol>
  <li>Click the <code>ComboBox</code> drop down button -- this displays the list of items and selects the text in the <code>ComboBox</code></li>
  <li>Type '5', '1' ... i.e. I'm looking to use autocomplete to search for 515, 516, etc.</li>
  <li>You'll see that the autocomplete window now appears ON TOP of the drop down list.  However if I mouse over, it's the obscured drop down window behind the autocomplete window that's receiving the mouse events, including the click.  So I think I'm clicking on an autocomplete item but actually clicking on something totally random that I can't see.</li>
  </ol>
  
  <p>Is this a bug in the <code>ComboBox</code>?  I'm using Windows 7 if that matters.  Am I configuring the <code>ComboBox</code>wrong somehow?</p>
  
  <p>Note also that using the KEYBOARD uses the autocomplete drop down.  So up/down arrow keys are using the front window, but the mouse is using the back window.</p>
  
  <p><a href="https://i.stack.imgur.com/z2YWS.png" rel="noreferrer"><img src="https://i.stack.imgur.com/z2YWS.png" alt="enter image description here"></a></p>