RadTreeView is virtualized and SelectionMode is set to "Extended". All ViewModels are selected and IsSelected of TreeViewitems is 2-way bound to IsSelected in the ViewModels. When clicking a TreeViewitem with Mouse, all other items are deselected. However, when scrolling we see that items are being prepared are not deselected - they are still selected.

This is due to a Limitation of the Virtualization mechanism - it does not know about the existance of the ViewModels and does not work with them. Virtualization works only with the Containers - the RadTreeViewItem.