The busy animation keeps running on the background when the busy indicator control gets unloaded (removed from the visual tree).

To work this around, set the IsBusy property of RadBusyIndicator to False in its Unloaded event handler.

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 };
    }
}