TreeView.HandleDragAndDrop fires twice

Hello,

I don't know why this happens but it's a huge pain.
I've overriden TreeView.HandleDragAndDrop:

Code (CSharp):

1. protected override DragAndDropVisualMode HandleDragAndDrop(DragAndDropArgs args)
2.     {
3.         if (args.performDrop)
4.         {
5.             if (args.dragAndDropPosition == DragAndDropPosition.UponItem)
6.                 Debug.Log("Twice??");
7.             else
8.                 Debug.Log("Once");
9.         }
10.  
11.         // code...
12.     }

In this method, I want to do an AssetDatabase.MoveAsset.
When I drag my file upon a folder and release the mouse button, the method seems to fire twice?
When it does, obviously my code raises an error because I already moved the asset the first time.
Is this really a wanted behaviour?