Currently, if you wrap RadAutoCompleteBox in a ScrollViewer (along with some other controls) and enable the vertical scrollbar of the child TextBox control, the scrolling doesn't bubble to the parent ScrollViewer when you reach the beginning (scroll up) or the end (scroll down) of the TextBox scrollbar.
Add an option or change the default behavior and allow the scrolling to bubble to the parent scrollbar. This behavior can be observed in the native TextBox control with an enabled vertical scrollbar.
For the time being, the MouseWheel event can be manually raised:
private void ScrollViewer_PreviewMouseWheel(object sender, MouseWheelEventArgs e)
{
if (sender is ListBox && !e.Handled)
{
e.Handled = true;
var eventArg = new MouseWheelEventArgs(e.MouseDevice, e.Timestamp, e.Delta);
eventArg.RoutedEvent = UIElement.MouseWheelEvent;
eventArg.Source = sender;
var parent = ((Control)sender).Parent as UIElement;
parent.RaiseEvent(eventArg);
}
}