TreeviewItem disappears after draggin it onto a grid

Question

I am dragging and dropping a Treeviewitem from a RadTreeview in my WPF/C# project. After a succesful drag and drop the node disappears from the treeview. How can I avoid this? which event handler to change for this? I am assuming that this should be done in teh treeview's drag event handler and nothing to do with the grid's drop event handler.