Actually the behavior of the RadAutoCompleteView is the correct one - FilteredItems collection is populated when the user starts typing and the filtering logic of the control is executed. There is an issue in the old AutoComplete that caused the FilteredItems to contain the complete list.
Still, you could accomplish the scenario with RadAutoCompleteView with some additional logic. Basically, you would need to use a converter inside the binding of the ListView ItemsSource, so that, when there are no filtered items inside the AutoCompleteView, return the complete list of its items.
I have attached a sample project to show you how this would work, please download it and give it a try.
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