Thank you for writing.
property is supposed to specify a value indicating whether the selected tree node remains highlighted even when the tree view has lost the focus. However, it doesn't work in RadTreeView
I have logged it in our feedback portal and I have added a vote for it on your behalf. You can track its progress, subscribe for status changes and add your comments on the following link - feedback item.
I have also updated your Telerik points.
I hope this information helps. Should you have further questions I would be glad to help.