Consider replacing the current touch gesture which starts drag operation. Now the gesture (tab and hold + move up) is not very intuitive. 

With Q2 2015 Release the DragDrop on touch device will work the following way. Hold down the finger on RadTreeViewItem, TouchIndicator circle appears and then you can move your finger to start the dragging.

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"

Change the selection on MouseLeftButtonUp instead of MouseLeftButtonDown.

DECLINED: Duplicate with https://feedback.telerik.com/Project/143/Feedback/Details/112812-treeview-perform-selection-on-mouseleftbuttonup

Setting these properties in the Legacy mode works as expected. The NEW DND mode will be the default one in Q2 2014.

Select a RadTreeViewItem with MOuse and in SelectionChaged event handler disable the RadTreeView. Then when you enable it programatically, the SelectedItems's foreground is wrong.

Available in LIB Version: 2015.2.720.

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.

When you tab through your application you can observe that when the focus moves to the TreeView it will focus the first TreeViewItem. However, when you change the ItemsSource collection of the TreeView at run-time you won't be able to tab through the TreeView or its first TreeViewItem at all.

Fixed in LIB version: 2014.2.0915

When you have a, for example, a RadSlider in a RadTreeViewItem and you try to move the Thumb of the slider, the drag events of the tree view item will be triggered. The same behavior is observed also when you have a TextBox instead of a slider and try to mark part of the text in it with the mouse.

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 DefaultImageSrc property doesn't show the image when it is set to a relative file path.
Reason for Decline: This is not actually a bug. When you set the DefaultImgSrc in XAML starting with "/" the Image is shown successfully. In WPF the relative image sources must begin with "/".

http://msdn.microsoft.com/en-us/library/aa970069%28v=vs.110%29.aspx 

RadTreeView is throwing an IndexOutOfRangeException when the host panel is resized. 
StackTrace:
 at Telerik.Windows.Controls.TreeView.IndexTree.CumulativeValue(Int32 endIndex) in c:\TB\105\WPF_Scrum\Release_WPF\Sources\Development\Controls\Navigation\TreeView\Virtualization\IndexTree.cs:line 271
   at Telerik.Windows.Controls.TreeView.TreeViewPanel.ExtendDesiredSize(ItemsControl itemsControl, Size stackDesiredSize, Int32 pivotIndex, Boolean before) in c:\TB\105\WPF_Scrum\Release_WPF\Sources\Development\Controls\Navigation\TreeView\Virtualization\TreeViewPanel.cs:line 2287
   at Telerik.Windows.Controls.TreeView.TreeViewPanel.MeasureOverride(Size constraint) in c:\TB\105\WPF_Scrum\Release_WPF\Sources\Development\Controls\Navigation\TreeView\Virtualization\TreeViewPanel.cs:line 1680

===
This item is declined because we are unable to reproduce such exception with our latest binaries.

BringIntoView and GetItemByPath are slow on trees with many nested levels (20-30).
In Q2 2014 these methods will be faster in scenarios with TreeView Lines.

When the data is bound to the RadTreeView the AutoScrollToSelectedItem doesn't work. The same behavior appears when the RadTreeViewItems are created declarative and the SelectedItem is set True on any of its root level items. 

Available in LIB version: 2014.3.1301

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.

RadTreeView or RadPanelBar has custom Style in which there is no ScrollViewer in the ControlTemplate. IsDragDropEnabled is set to true. When dragged item is dragged above the tree/panelbar - null reference exception occurs in RadTreeView.AutoScrolling.cs.

When the RadTreeViewItem (or the RadTreeView) is disabled and after a delay is enabled again it should go in "Normal" state. Now the control preserves its state, hence you are able to send more than one RadTreeViewItem in "Hovered" state.

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.

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.

Reason for declination: 
The feedback item is declined due to duplication with the one below:
http://feedback.telerik.com/Project/143/Feedback/Details/113789-treeviews-scrolling-does-not-work-if-the-trees-width-is-set-to-0-and-then-back
Please follow it instead. 

When the IsLineEnabled property is set to True and there are more than 3 levels of hierarchy, the lines look jagged.

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