protected override void OnDragLeave(EventArgs e)
{
// is there a current drop-target node?
if (_dropTargetNode != null)
{
// remove highlighting from drop target node
HighlightNode(_dropTargetNode, false);
SetInsertMark(_dropTargetNode, DragDropPosition.Default);
}
// clear the drop target node
_dropTargetNode = null;
_dropEffect = DragDropEffects.None;
_dropPosition = DragDropPosition.Default;
base.OnDragLeave(e);
}