When the ItemsPanel is set to VirtualizingStackPanel which Orientation is set to Horizontal, selecting an item moves it to the rightmost position.

Available in LIB version 2016.3.1017, it will be also available in the 2016 R3 SP1 release. 

The SelectionMode must be Multiple.

When the control is initially Collapsed setting the SelectedIndex does not update the SelectedItem property of the control and vice versa.

If a dragged item is not over an existing item of the ListBox control the drop cue is not displayed. By default it should be rendered after the last item in the ListBox control.

Available in the 2014 Q2 Release.

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.