title: How to preserve Vaadin Tree container items order?
body: <p>I have <code>Vaadin 7</code> <code>Tree</code> with <code>HierarchicalCOntainer</code> which contains items in some order (reordered through <code>.moveAfterSibling()</code>.</p>
  
  <p>When I try to get their <code>ID</code> collection I get them into order I have originally inserted, not the order they are shown.</p>
  
  <p>I have checked both <code>container.getItemIds()</code> and <code>.firstItemId()</code> / <code>.nextItemId()</code>. Both do not match the order I see on the screen.</p>
  
  <p>What do I do wrong way?</p>