title: RichEditBox crashes in certain condition.
body: <p>Rich edit box crashes for me if I try to set the fontsize to it.</p>
  
  <p>C# code:</p>
  
  <pre><code>REB_Value.Document.SetText(TextSetOptions.None, "Company  Name,  \nStreet name with zip code. \n123-456-7890");  
  </code></pre>
  
  <p>The XAML: </p>
  
  <pre><code> &lt;StackPanel Orientation="Vertical"&gt;
         &lt;TextBlock Text="Lable for this Field:" Style="{StaticResource TextBlockStyle}"/&gt;
         &lt;RichEditBox Name="REB_Value"            
                      ContextMenuOpening="OnContextMenuOpening" 
                      Style="{StaticResource MyStyle}" 
                      SelectionChanged="OnSelectionChanged" &gt;
        &lt;/RichEditBox&gt; 
   &lt;/StackPanel&gt;
  </code></pre>
  
  <p>Style:</p>
  
  <pre><code>&lt;Style x:Key="MyStyle" TargetType="RichEditBox"&gt;
          ...
          &lt;Setter Property="BorderBrush" Value="Transparent"/&gt;
          &lt;Setter Property="BorderThickness" Value="{StaticResource TextControlBorderThemeThickness}"/&gt;
          &lt;Setter Property="FontFamily" Value="{StaticResource ContentControlThemeFontFamily}"/&gt;
          &lt;Setter Property="FontSize" Value="14"/&gt;
         ...
      &lt;/Style&gt;
  </code></pre>
  
  <p>The page renders/Loads if I remove the property <code>&lt;Setter Property="FontSize" Value="14"/&gt;</code>  or If I put an /n at the end of my string
   ie: <code>"Company  Name,  \nStreet name with zip code. \n123-456-7890\n"</code></p>
  
  <p>There are other RichEditBoxes which works fine,
  eg:</p>
  
  <pre><code>SomeOtherREB.Document.SetText(TextSetOptions.None, "123456789"); 
  </code></pre>
  
  <p>I don't understand why this is happening? </p>