Hello Almir Kazazic,
Thank you for reporting this issue.
To avoid this behavior you, should call InvalidateNode
after changing the tool tip text of the node.
this.radTreeView1.Nodes.ToolTipText = "new node tooltip text;
this.radTreeView1.InvalidateNode( this.radTreeView1.Nodes );
We will implement this behavior in our upcoming release (Q3 2007). This will make InvalidateNode no longer necessary. Your Telerik points have been updated.
Hope that helps. Contact us again if we could be of further assistance.
the Telerik team