EditorUtility.InstantiatePrefab and assets not working ?

in a simple Post Processor I want to instantiate the asset while keeping connection and I use

Code (csharp):

1.  
2.     void OnPostprocessModel (GameObject modelRoot)
3.     {
4.         GameObject assetInstance = EditorUtility.ReconnectToLastPrefab(assetInstance) as GameObject;
5.         }
6.  

It does not create an instane in the scene.
GameObject.Instantiate does however work.

Is there a workaround ?