Can't get document to display in EditorDocumentViewer

I have an EditorDocumentViewer placed as content to a BackstageTab labeled "Print".   I populate the Document property with the a FixedDocument created by the actively displayed syntaxeditor using the "editor.PrintSettings.CreateFixedDocument(editor)" method.   However the document does not display on the screen.  All of the buttons become active and when I click the Print button the correct document prints.  Here is the snipped of code I use to populate the Document property:

      private void PrintBackstageTabBorder_IsVisibleChanged(object sender, DependencyPropertyChangedEventArgs e) {
         var visible = e.NewValue as bool?;
         if(visible != null && (DockingSite.ActiveWindow != null && (bool) visible)) {
            var editor = DockingSite.ActiveWindow.Content as SyntaxEditor;
            if(editor != null) {
               editor.PrintSettings.DocumentTitle = editor.Document.FileName;
               editor.PrintSettings.IsDocumentTitleMarginVisible = true;
               editor.PrintSettings.IsLineNumberMarginVisible = App.Preferences.LineNumberMargin;
               editor.PrintSettings.IsPageNumberMarginVisible = true;
               editor.PrintSettings.IsSyntaxHighlightingEnabled = true;
               editor.PrintSettings.IsWordWrapGlyphMarginVisible = true;
               editor.PrintSettings.IsWhitespaceVisible = App.Preferences.Whitespace;

               Viewer.Document = editor.PrintSettings.CreateFixedDocument(editor);
            }
         }
      }

And here is XAML for the EditorDocumentViewer:

               <ribbon:BackstageTab x:Name="PrintBackstageTab" Header="Print" KeyTipAccessText="P">
                  <Border x:Name="PrintBackstageTabBorder" Style="{StaticResource ContentBoxBorderStyle}" IsVisibleChanged="PrintBackstageTabBorder_IsVisibleChanged">
                     <syntaxeditor:EditorDocumentViewer x:Name="Viewer"
                                        Margin="15,0,0,0"
                                        DockPanel.Dock="Right" HorizontalContentAlignment="Stretch" VerticalContentAlignment="Stretch" />
                  </Border>
               </ribbon:BackstageTab>

Any help would be appreciated.   This works in the sample provided with the controls, but I can't seem to get it to work for me though.