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.

It was suggested that the ItemTemplates in the tree view should update when the item template selector or the item template is changed.

This will be hard to implement properly because of the numerous ways in which a template can be set. A naive implementation is more doable, though we are not notified when the ItemTemplate property changes
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Reason for marking this Declined: Too little information, too old item (5.5 years) with too litle votes.

Add a possibility to disable selection of RadTreeViewItem.

An appropriate ItemEditTemplate can be generated when the DisplayMemberPath property is used.

The request is related to the method AddItemByPath - To build the whole hierarchy not only to add the string after last separator.

Too specific requirement that could be implemented as application logic.

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