Rendering issues occure when using Hierarchical virtualization mode and bring into view.
The issue is hit in both platforms - WPF and Silverlight. 

RadTreeViewItem.AutomationProperties.Name is not read correctly since version 2011.2

In a virtualized TreeView, after ExpandAll and scroll operations, there are gaps in the TreeViewPanel.

System.Windows.Media.Animation Warning is apparent during DragDrop in the TreeView in WPF. 

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.

Modify the SelectionChanged event logic so that the event is only fired once - exposing both the RemovedItems and AddedItems collections.

Improve selection performance.

The scroll position resets when the measure of the treeview panel is fired for some reason.

For example, when the RadTreeView is placed inside a RadPanelBarItem and the RadPanelBar's ScrollViewer is disabled, resizing the RadPanelBar resets the RadTreeView scroll position. 

Ability to validate if there are selected,checked, expanded items, if a node has items

When placed in grid column with Auto width and had its own width set to Auto, the RadTreeView does not scroll.

The Horizontal ScrollBar cannot be hidden/disabled in certain situatations, for example when TreeView is inside RadPanelBarItem

Expose IsDropBeforeAllowed, IsDropAfterAllowed and IsDropInsideAllowed properties in order to facilitate the implementation of complicated drag/drop scenarios in MVVM scenarios.

Update: The suggested approach would be to use an attached behavior for DragDropManager.DragOverEvent in order to change the default TreeView behavior.
DropAction property of a TreeViewDragDropOptions instance could be used to customize the drop operation.
Also, the DropPosition property of the TreeViewDragDropOptions instance could be used to check current drop case.
An instace of TreeViewDragDropOptions could be retreived from DragOverEvent event arguments.

We have RadContextMenu in RadTreeView when we press the App key or shift+F10 the context menu opens as intended but it triggers the parent TreeViewItem hover effect

Scenario: Databound TreeView with IsSelected bindings between item and container. Adding a selected data object to the ItemsSource does not fire the Selected event.

This will solve scenarios in which user wants to add new items somewhere (inner level, outside the ViewPort ) in virtualized treeview and then wants to begin edit these items (or focus them , select them). 
There is currently no mechanism to detect when the new items are ready (measured / completely generated), ItemsPrepared for example passes before the OnApplyTemplate of the RadTreeViewItem.

When IsVirtulizing is set to true and there are many items in the tree view pressing several times PageUp key brings the view port to the beginning of the tree rather to the previous page.

Cannot properly scroll when using StackPanel as ItemsPanel.

Support DragCue and vertical PreviewDropLine when TreeView renders its items horizontally

Currently when the UI Virtualization is enabled, the RadTreeView sets the IsExpanded property of the RadTreeViewItems to False when they don't have any children. We can add a mechanism by which this can be stopped. 

BindingExpressionError occurs in situations  when the tree is virtualized and TemplateSelectors are used