title: WPF RichTextBox autoscroll not works when add Document.Blocks in Background worker
body: <p>I use WPF rich text box to log data process:</p>
  
  <pre><code>&lt;ScrollViewer&gt;
    &lt;RichTextBox x:Name="rtbLog" IsReadOnly="True" /&gt;
  &lt;/ScrollViewer&gt;
  </code></pre>
  
  <p>Code-behind I use BackgroundWorker to process data and update log by ProgressChanged event handler:</p>
  
  <pre><code>Private Sub WorkerReport(sender as Object, e as ProgressChangedEventArgs) Handles Worker.ProgressChanged
    Dim para as New Paragraph
    para.Inlines.Add(New Run(...some data))
    rtbLog.Document.Blocks.Add(para)
    rtbLog.ScrollToEnd()
  End Sub
  </code></pre>
  
  <p>New data is appends successfully, but RichTextBox don't scrolls to end. </p>
  
  <p>What is the problem, why my solution is not working?</p>
  
  <p>Thank you for any advise.</p>