I'm not sure where enhancement requests go so I figure I'll start here:
RadListVIew.SelectedItem is intended to represent the last item added to the SelectedItems collection. This paradigm makes sense when SelectionMode is set to Multiple. However, when SelectionMode is set to Single, implementers should be free to ignore the SelectedItems collection altogether set set SelectedItem. You can easily handle this feature by making the setter of SelectedItem public and in that setter, determining if SelectionMode is Single and then allowing the set to take place. If it is not set to Single, throw an exception or do something else to let implementers know that this action is disallowed.