After selection autocomplete uses the data within TextSearchPath for display. We search many fields so this output is less than ideal. DisplayMemberPath or a SelectedItemTemplate would be better.

RadAutoCompleteBox respects the changes in the SelectedItems collection, but it does not raise the appropriate slection changed event.
Workaround: Use an observable collection and subscribe to its CollectionChanged event.

Expose the Textbox's MaxLength property to limit text input on the RadAutoComplete SearchText Property

While the SelectedItem is not null setting it to null and then returning the SelectedItem causes the drop down of the control to be opened