When RadSpreadsheet is placed inside a data template and the Workbook property is bound, the binding fails. 

In the Convert() method of the debug converter, the proper value is set. However, an empty workbook is displayed in the view.

RadSpreadsheetFormulaBar has a drop down list that shows the named ranges in the document. If a named range contains an underscore character (ex: Income_Amount), the associated item in the drop down won't display the underscore (ex: IncomeAmount).

To workaround this, you can use a global Loaded event handler of RadMenuItem and override the Header content with a TextBlock.

static MainWindow()
{
    EventManager.RegisterClassHandler(typeof(RadMenuItem), RadMenuItem.LoadedEvent, new RoutedEventHandler(OnMenuItemLoaded));
}

private static void OnMenuItemLoaded(object sender, RoutedEventArgs e)
{
    var menuItem = (RadMenuItem)sender;
    if (menuItem.DataContext is DefinedName context)
    {
        menuItem.Header = new TextBlock() { Text = context.Name };
    }
}