When the ItemsSource of the control is changed to a new collection the old selected items are cached and if a collection containing the old selected items source is set as ItemsSource the cached items are restored. Make it possible to disabled this functionality per control. Available in the 2017 R1 Release (2017.1.117).
Implement IsSynchronizedWithCurrentItem property in order to disconnect the connection with CollectionViewSource.
Add SelectedItemsSource property which can be bound to a collection in the view model. In this case when the RadListBox is in Multiple/Extender mode, the selection can be manipulate from the ViewModel.