DataTriggers that apply DefaultImageSrc, ExpandedImageSrc don't work when the TreeView is virtualized.
Reason for deletion:
The workaround is easy - just bind the DefaultImageSrc, ExpandedImageSrc to string properties from the ViewModel.
Also, a possible fix would slow down the virtualization process in the RadTreeView.

Dynamic change of the DataContext does not reflect the DataContext of the TreeViewItems.

The XAML team has recently reviewed this issue and will not be addressing it as at this time the team is focusing on the bugs impacting the highest number of developers. If you have encountered this issue and it is blocking for your work please contact us through the support ticketing system with details on your setup and a reference to this item.

Add 'None' to the selection mode enum

The children count is read incorrectly by MS Narrator

The CheckedItems  collection is not cleared when ItemsSource is changed.

Please consider CheckedItems as not supported collection in RadTreeView. In DataBinding scenarios , use the approach described in the following article:
http://docs.telerik.com/devtools/wpf/controls/radtreeview/how-to/howto-tri-state-mvvm.html 
This way you will be able to create CheckedItems property in your ViewModels.

The XAML team has recently reviewed this issue and will not be addressing it as at this time the team is focusing on the bugs impacting the highest number of developers. If you have encountered this issue and it is blocking for your work please contact us through the support ticketing system with details on your setup and a reference to this item.

The TreeView doesn't update the TriState of the parent item when an item is dragged and dropped.

In databound scenario the built-in checkbox and the tri-state mode are considered not supported and users are prompted to use checkbox in itemtemplate with 3state logic in the viewmodels.
http://docs.telerik.com/devtools/wpf/controls/radtreeview/how-to/howto-tri-state-mvvm.html 

The XAML team has recently reviewed this issue and will not be addressing it as at this time the team is focusing on the bugs impacting the highest number of developers. If you have encountered this issue and it is blocking for your work please contact us through the support ticketing system with details on your setup and a reference to this item.

When the ScrollViewer of a virtualized TreeView is visualized the bindings of the TreeViewItem are broken.

We are closing this one because of duplication with the following item => http://feedback.telerik.com/Project/143/Feedback/Details/112754-treeview-bindingexpressionerror-occurs-in-situations-when-the-tree-is-virtualiz 

When the TreeView's ScrollViewer is Visible, changing the tree's width to 0 them back to Auto breaks the scrolling function of the ScrollViewer.
The workaround is to make the TreeView Collapsed before setting the Width to 0 and make it Visible before setting the Width back to Auto.

Another workaround: Use visibility instead of Width=0.

The TreeView should be able to figure out the Old / NewValue for its event args during editing.
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Reason for deletion. In databound scenarios e.OldValue and e.NewValue refer to the same instance of the ViewModel which is expected. 

Saving the state of the ViewModels means creating an entire deep copy of the ViewModel. We believe there is no such control in the framework to save the states of its ViewModels during editing.

We have to admin, introducing public properties OldValue and NewValue of type objects for these event args is a bad design. This is a bug since these are public but we won't fix it due to the complexity (described above).

There should be a way to exclude the partially checked items from the CheckedItems collection. 
A a property can be added to specify whether they will be included.

Edit: Please avoid using this collection because it ihas never been implemented completely in the RadTreeView. In DataBinding scenarios, you can use CheckBox in the ItemTemplate of the RadTreeView. Approach can be found here =>
http://docs.telerik.com/devtools/wpf/controls/radtreeview/how-to/howto-tri-state-mvvm.html 
CheckedItems colelction can be implemented in the ViewModels, instead of using the built-in property.

The XAML team has recently reviewed this issue and will not be addressing it as at this time the team is focusing on the bugs impacting the highest number of developers. If you have encountered this issue and it is blocking for your work please contact us through the support ticketing system with details on your setup and a reference to this item.

It should be possible to collapse certain items to filter them out. This should not affect the look or functionality of the 

This is already implemented => you can use the ItemVisibility property of the RadTreeView.

This issue is applicable to Silverlight ONLY!

We have a RadTreeView with following properties IsLoadOnDemandEnabled="True", IsVirtualizing="True" and SelectionMode="Extended" set.
We select an element, collapse his parent and select another item. At this point if we expand the previously parent, both the newly selected item and the the first selected item are selected.
It is not correct the first item to preserve its selection state.

The XAML team has recently reviewed this issue and will not be addressing it as at this time the team is focusing on the bugs impacting the highest number of developers. If you have encountered this issue and it is blocking for your work please contact us through the support ticketing system with details on your setup and a reference to this item.

The built-in drag drop mechanism works with the containers of the items and makes a snapshot of them for the DragVisual. Thus, dragging multiple selected items that are not present in the viewport is not possible.

Adding a Checked RadTreeViewItem from code behind checks its parent which is xaml defined.
On loaded event of The RadTreeView adding a parent item and checked child item with Dispatcher.beginInvoke checks the parent.

The XAML team has recently reviewed this issue and will not be addressing it as at this time the team is focusing on the bugs impacting the highest number of developers. If you have encountered this issue and it is blocking for your work please contact us through the support ticketing system with details on your setup and a reference to this item.

The CheckBox`s CheckMark is mirrored when the RightToleft FlowDirecttion is set in the RadTreeView

Reordering checked items using the drag/drop implementation in a TreeView with IsTriStateMode=False, sets the parent item in an indetereminate state

Improve the synchronization between the TreeView.IsOptionElementsEnabled with the TreeViewItem.OptionType property. In a scenario where the TreeViewItem.OptionType property is databound, changing the TreeView.IsOptionElementsEnabled property doesn't respect the databound values of the TreeViewItem.OptionType.
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Reason for deletion: These  proeprties are marked obsolete.

Collapse a RadTreeViewItem when all its children are dragged elsewhere. This is needed in scenarios where the RadTreeViewItem DefaultImageSrc and ExpandedImageSrc properties are set, and you want to revert back to the DefaultImageSrc once all children of the item are dragged to other positions.

The TreeViewPanel doesn't display the TreeViewItems when the TreeView ItemsPresenter ControlTemplate element is wrapped in a Border or Grid control.

Declined.

Changing the default control template of our controls is risky, every template part has its purpose and usually it is used in code behind. 
We cannot support such template changes to not reflect the main features such as virtualization,scrolling, fast performance.

Create localization resources for the DropActionText in the TreeViewDragVisual element. The localization resources should work as the TextDropAfter, TextDropBefore, TextDropIn and TextDropRoot properties used to work in the Legacy mode of the RadTreeView DragDrop.