title: Extended WPF Toolkit RichTextBox display text vertically
body: <p>I'm trying to bind a rich content (RTF format) to a rich text box (of Extended WPF Toolkit) via its Text property like this</p>
  
  <pre><code>&lt;extToolkit:RichTextBox x:Name="rtbKIContent" Margin="8,8,8,8" 
                                      IsEnabled="{Binding IsEditable}"
                                      Text="{Binding Content}"&gt;
                  &lt;extToolkit:RichTextBox.TextFormatter&gt;
                      &lt;extToolkit:RtfFormatter&gt;&lt;/extToolkit:RtfFormatter&gt;
  
                  &lt;/extToolkit:RichTextBox.TextFormatter&gt;
                  &lt;extToolkit:RichTextBoxFormatBarManager.FormatBar&gt;
                      &lt;extToolkit:RichTextBoxFormatBar /&gt;
                  &lt;/extToolkit:RichTextBoxFormatBarManager.FormatBar&gt;
  &lt;/extToolkit:RichTextBox&gt;
  </code></pre>
  
  <p>Sometimes it works just fine, but there are circumstances that they just display the text vertically like this.</p>
  
  <p><img src="https://i.stack.imgur.com/C4HWp.png" alt=""></p>
  
  <p>I don't know what's wrong with it...What should I do to make it display text from left to right like normal? </p>