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.

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.

When TreeView is placed inside floating VS ToolWindow and item is selected the visual state remains unchanged after focus leaves the TreeView.

When the RadTreeView is virtualizaed, the images are  not shown. This works when the tree is bound to collection of objects and the DefaultImageSource is bound.

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.

When two equal objects are used in the source collection, the first is always selected when you try to select the others.

Workaround when TreeView is not databound.

Instead of adding objects directly in the TreeView's Items Collection, add RadTreeViewItems.
For Example, instead of
 treeView.Items.Add(1), 
treeView.Items.Add(2)

do

 treeView.Items.Add(new RadTreeViewItem(){Header = 1}, 
 treeView.Items.Add(new RadTreeViewItem(){Header = 2}

Workaround when TreeView is databound.

For example , if we databind the treeview to collection of DataItems and some dataitem is located in multiple places in the source collection.
Solution => Wrap the DataItem class in new class - DataItemWrapper. It can hold the underlying DataItem, add additional property  (for exampel ID) and override the Equals and GetHashCode methods.
This way different DataItemWrapper objects can hold equal DataItem objects. In such way if you bind the treeview to collection of DataItemWrappers the selection will be successful.

DECLINED:
The XAML team recently reviewed this bug  and won't be adressing it in future. It can be actually considered as feature request because selection should have notion for selected containers.
Unfortunately, the initial code design of the RadTreeView does not have such notion and the complexity of adding such feature now is very big.

a) Using WCF RIA Services
b) Using QueryableDomainServiceCollectionView
c) Using TreeView with above two
d) Including LoadOnDemand
e) Using "Prepared Item"

Items are lost after reexpanding when TreeView is Virutalized and items are set in XAML.
Currently the TreeView does not support virtualization when using XAML items.

Reason for Decline: Virtualization is not supported in non-databound treeviews.

Dynamically change of the theme of the RadTreeViewItems cannot be achieved.

Reason for decline:
The bug is outdated. Every RadTreeViewItem can be Styled via its Style property or the ItemContainerStyle of the RadTreeView.

SelectedItems collection not updated when items are removed

Too many TreeViewItems are created internally when using virtualization. This causes the tree to consume large amount of space when performing virtualization intensive tasks like CollapseAll or ExpandAll.

The XAML team recently reviewed this issue and will not be addressing it.
On ExpandALL / CollapseALL virtualization creates / recycles / reuses containers - RadTreeViewItems. You cannot be sure when the GarbageCollector will free up the currently unused containers.
Also after even number of invocations (ExpandAll + CollapseAll), the containers that are not freed up from memory is not increasing - it is constant which means there is no memory leak to worry for.

Ability to temporary view particular element as root item. Functionality have to be similar to "View this as root" in the Solution Navigator window in Productivity Power Tools for Visual Studio.

This is too custom requirement that can be implemented as application logic. 
Setting fildetered itemssource and preserving the current itemssource could be a possible solution.

Binding to IsChecked property doesn't work in TwoWay mode (ConvertBack doesn't work).

Declined.
IsChecked / CheckState are supported only in xaml-defined RadTreeViews. In databinding scenarios use the approach described here =>
http://www.telerik.com/help/wpf/radtreeview-howto-tri-state-mvvm.html

Showing a message box in the DoubleClick event handler in a D&D enabled RadTreeView starts a drag operation unexpectedly.

Closing this one - we are not able to reproduce it with our latest binaries.

Allow selecting and unselecting items on right click when the SelectionMode is Multiple/Extended.

Reason for decline: This can easily be implemented as application logc using th MouseRightButtonDown event of the RadTreeView.

When using binding to CheckState property and TriStateMode is enabled the checking of parent (its business object) does not affect unrealized childrens' CheckState, because the bindings have greater priority than the TriState logic. Same in the other direction - checking the child has no effect over the parent.

Marking this as Declined.
TriState Mode is supported in XAML-defined or code behind defined trees with direct creation of 3Viewitems. 
In DataBound scenarios, 3-State should be created by the user with ViewModels as described in this help article.

http://www.telerik.com/help/wpf/radtreeview-howto-tri-state-mvvm.html

Programmatically reorder items with animation.

Declined. This could be implemented as application logic. The requirement is too specific to be included in the publi API of the RadTreeView.

Expand bottom up.
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Reason for deletion: 0 votes for more than 4 years. 
Users can invoke in a loop ExpandItemByPath in order to achieve expanding from bottom to top.

Sometimes when using the treeview in TriStateMode I wish I could have the ability to uncheck all the children of an indeterminate parent with one click. Currently when a parent is in indeterminate mode and you click on it, it will activate it and all it's 
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Reason for Decline:
This is a custom requriement and could be implemented as application logic based on this example:
http://www.telerik.com/help/wpf/radtreeview-howto-tri-state-mvvm.html

We have a RadTreeView. There is no horizontal scrollbar.
We edit a node's header to a longer string and a horizontal scrollbar appears.
If we edit again the node's header to a shorter string, the horizontal scrollbar remains even it isn't needed anymore.

UPDATE:
There is a similar problem with the height of a RadTreeViewItem.
If we edit the RadTreeViewItem's content to become at least of two lines - the height of the item is increased, which is expected.
But if we re-edit this item's content to be on one line only - the height of the item remains larger, which is incorrect.
Please note, that this issue is observed ONLY on sub-items not on the parent nodes.

This seems not reproducible  with R3 2016 version of RadTreeView.
Please open a new support ticket with details regarding this issue if you encounter it.

When a copy of the Control Template of the RadTreeView is edited in Blend, the followin error is thrown: TargetName property cannot be set on a Style Setter.

Reason for closing: The bug is not reprodible with VS 2012, WPF 4.5 and latest official version of telerik UI for wpf.