title: Flex Tree vertical scrolling problem
body: <p>I am using mx:Tree (in Flex 4), and assigned a customised MXTreeItemRenderer for every items. As the TreeItemRenderer contains a list with tileLayout, which means the height of every row is variable. So I have to set the tree's "variableRowHeight to true. When I was testing the tree, everything went well. But when I was using the vertical scroller, I met some problems: </p>
  
  <ol>
  <li><p>The scroll bar did not move to the position I want. When I was scrolling the content, the scroll bar sometimes scrolled to a unwanted position (e.g. the head of the tree). When there are more rows, the problem is more obvious.</p></li>
  <li><p>When I was scrolling the tree, the images were flicking all the time. That means, the images are reloading I guess. any help?</p></li>
  </ol>
  
  <p>Is there anyone who can help me solve the problems? many thx :)</p>