The vertical scroll cannot be moved via the mouse wheel or by clicking on the scrollbar's thumb after the End key is pressed. This is reproducible ONLY if the UI virtualization is enabled and if there are many items (500-1000+).

The TreeViewItems are expanded and collapsed on MouseLeftButtonUp which leads to an expand/collapse operation even if the MouseLeftButtonDown event was fired by another element. This can be easility reproduced if you hold down the mouse left button over any element outside the RadTreeView and then releasing it over any RadTreeViewItem when the RadTreeView IsExpandOnSingleClickEnabled is True.

It can also be reprorduced with the following steps:
1) left click on a node and hold the mouse button down
2) release the mouse when over a non-selected node that has children.
The result is expanding/collapsing the unselected node.

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.

Use virtualization in hierarchical mode. Select a RadTreeViewItem that has parent. Move it somewhere in the source collection of the parent programmatically - reorder or sort. The item will remain in Museover State forever.

Perform the same steps with Recycling mode, there might be missing RadtreeViewItems (not rendered at all) after the sort / reorder operation.

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.

TreeView Virtualization Mode is Recycling (the default one). In the ItemTemplate there is a RichTextBox with HtmlFormatProvider. Changing ItemsSource of the TreeView runtime produces null reference exception in TreeViewPanel.CleanupRange().
The Exception comes from the RecyclingItemContainerGenerator.Recycle method (http://msdn.microsoft.com/en-us/library/cc452208(v=vs.110).aspx). 
As a workaround if applicable, user can use the HierarchicalVirtualization mode:
    <telerik:RadTreeView  telerik:TreeViewPanel.TreeVirtualizationMode="Hierarchical"

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

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

RadTreeView and RadTreeViewItem ExpandAll() method sets the IsExpanded property to True to all items even if an Item has no children to display. This causes an issue when using the DefaultImageSrc and ExpandedImageSrc properties as the last-level items will be displayed with an ExpandedImageSrc as their IsExpanded property it set to True. However, as these items have no children, they should use the DefaultImageSrc.

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

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

RadTreeView is virtualized and we use ItemContainerStyleSelector. The style selector select styles which set have ExpanderStyle property. The ExpanderStyle is not applied.

There is an attached project which can be used as a possible workaround,

Available in Official Release R3 2016.

REOPEN:

The bug will be re-opened from 5 Dec 2016 internal build as well as in the official R3 2017 release.
We reverted the fix for this bug due to performance hit we found in R3 2016.
The workaround suggested in the attached project is still valid.

The children count is read incorrectly by MS Narrator

Cannot properly scroll when using StackPanel as ItemsPanel.

When the FlowDirection is RightToLeft, the vertical lines of the control aren't properly aligned.

The issue is not reproducible with R3 2016 Release.

Root level items ItemTemplate is incorrectly set after virtualization when using HierarchicalDataTemplate with ItemTemplateSelector.
This causes the second level items to use incorrect data template.

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

When BringIntoView is called while an item is expanding the BringIntoView target item may appear on the screen but be animated away from it. The TreeView will not retry to bring it into view again.

Ideally the TreeVeiw should re-focus on the last BringIntoView target if possible once the animation is complete.

Currently there are two workarounds:
- Turn off the animations while expanding if BringIntoView will be called
- Call BringIntoView for the given item once the animations has completed.

Show tooltip when node (the Header of the RadTreeViewiItem) is clipped.

You can check a possible implementation in this SDK sample:
https://github.com/telerik/xaml-sdk/tree/master/TreeView/ShowTooltipWhenNodeIsClipped 

When value types are inserted in the Items collection of RadTreeView and root values are duplicated in the children a StackOverflowException is raised after a call to ExpandAll.

The XAML has recently reviewed the status of this issue and won't be addressing it in future releases.
This is a design limitation - RadTreeView does not support duplication of value types in its Items / ItemsSource collections. 
This potentially can cause troubles with virtualization / selection / expandALL features.