The dropdown is missing because the element that holds the items doesn't have its ItemsSource set. This is the ListBox named PART_ListBox
in the RadAutoCompleteBox ControlTemplate you just need to set the ItemsSource the following way and it will start working as expected:
Hope this will help you.
TRY TELERIK'S NEWEST PRODUCT - EQATEC APPLICATION ANALYTICS for WPF.
Learn what features your users use (or don't use) in your application. Know your audience. Target it better. Develop wisely.
Sign up for Free application insights >>