title: JComboBox content disappear once I select one
body: <p>I have a JCombobox whose content is populated this way:</p>
  
  <pre><code>List&lt;MyClass&gt; l = getList();
  for(MyClass ll : l)
    combo.addItem(ll.toString());
  combo.setSelectedIndex(0);
  </code></pre>
  
  <p>Everything's ok till I click on combo in order to show item list: when I click selected item disappears (but list appears) when I select an item on list whole combobox disappears!!
  Why?</p>