title: Virtualizing WPF Wrap Panel Issue
body: <p>There are not very many options for a virtualizing wrap panel for use in WPF.  For one reason or another MS decided to not ship one in the standard library.</p>
  
  <p>If anyone could be so bold as to provide a crowd source answer (and explaination) to the first work item on the following codeplex project, I would greatly appreciate it:</p>
  
  <p><a href="http://virtualwrappanel.codeplex.com/workitem/1" rel="noreferrer">http://virtualwrappanel.codeplex.com/workitem/1</a></p>
  
  <p>Thanks!</p>
  
  <hr>
  
  <p>Summary of issue:</p>
  
  <p>I've recently tried using the virtualizing wrappanel from this project and have encountered a bug. </p>
  
  <p>Steps to reproduce:</p>
  
  <ol>
  <li>Create listbox.</li>
  <li>Set the virtualizing wrappanel as the itemhost in a listboxpanel template.</li>
  <li>Bind the itemsource of the listbox to an observable collection.</li>
  <li>Remove an item from the backing observable collection.</li>
  </ol>
  
  <p>The Debug.Assert fails (Debug.Assert(child == _children[childIndex], "Wrong child was generated");) in MeasureOverride, and continued execution results in a null exception in the Cleanup method [see attached screenshot]. </p>
  
  <p>Please let me know if you are able to correct this.</p>
  
  <p>Thanks,</p>
  
  <p>AO</p>
  
  <hr>
  
  <p>Code:</p>
  
  <p><a href="http://virtualwrappanel.codeplex.com/SourceControl/list/changesets#" rel="noreferrer">http://virtualwrappanel.codeplex.com/SourceControl/list/changesets#</a></p>
  
  <p><a href="http://virtualwrappanel.codeplex.com/Project/Download/AttachmentDownload.ashx?ProjectName=virtualwrappanel&amp;WorkItemId=1&amp;FileAttachmentId=138959" rel="noreferrer">alt text http://virtualwrappanel.codeplex.com/Project/Download/AttachmentDownload.ashx?ProjectName=virtualwrappanel&amp;WorkItemId=1&amp;FileAttachmentId=138959</a></p>