HideAndDontSave does not work when creating Prefab...

In Unity 4.5, I have a problem where a GameObject with the flags: HideAndDontSave shows up in the hierarchy.

I have an editor extension that allows to pick a component that can be dragged into the project panel to create a Prefab. The simplified code looks like so:

 void CreateDragAndDrop(string new_object_name)
 {
                 GameObject go= new GameObject(new_object_name);
                 go.hideFlags = HideFlags.HideAndDontSave;
                 DragAndDrop.PrepareStartDrag();
                 DragAndDrop.objectReferences= new UnityEngine.Object[1]{go};
                 DragAndDrop.StartDrag(new_object_name);
                 MemoryPool.DelayedDestroy(go);       // This service will destroy the object after it is not used for a period of time.
 }
 

In the Hierarchy...

When the drag is performed and ended inside the project panel, a Prefab is created but the GameObject is also visible in the hierarchy.

I can understand that the Prefab clones the 'go' but why does it now show in the hierarchy?

TAGS: Prefab, HideFlags, HideAndDontSave, DragAndDrop

NOTE: I had to put the TAGS in the text because the system does not allow me to create new tags and believe it or not Prefab does not exist; HideFlags does not exists; DragAndDrop does not exists ..... This is to wonder if we are in the Unity forum !!!