Saved PackedScene is not the same as original - misunderstanding about ownership perhaps ?

Question

When loading a previously saved PackedScene, I do not get the same scene as the original.

I have the following node tree ...
Spatial
- InstancedScenes

The following script is attached to the Spatial node

extends Spatial

const MyScene = preload("res://MyScene.tscn")

onready var node_to_be_packed = $InstancedScenes

func _ready():

#Create an arbitary sequence of instances of MyScene of different size
    for offset in range(0,4):
        var this_scene = MyScene.instance()
        this_scene.get_node("MeshInstance").translation = Vector3(0.0, 0.0, 1.5*float(offset))
        this_scene.get_node("MeshInstance").mesh.size = Vector3(0.5, 0.1, 0.1+0.2*float(offset))
        node_to_be_packed.add_child(this_scene)

#For convenience, to visualise the result
    var this_camera = Camera.new()
    add_child(this_camera)
    this_camera.translation = Vector3(1.0,3.0,6.0)
    this_camera.rotation_degrees = Vector3(-45.0, 0.0, 0.0)

#Now recursively assign 'node_to_be_packed' as the owner for all sub-nodes
    set_node_owner(node_to_be_packed, node_to_be_packed)

#And save the packed scene
    var package = PackedScene.new()
    var _result = package.pack(node_to_be_packed)
    var _error = ResourceSaver.save("res://packedscene.tscn", package)

#Recursive function to set node owner for all sub-nodes
func set_node_owner(this_node:Node, node_owner:Node)->void:
    for child in this_node.get_children():
        child.owner = node_owner
        set_node_owner(child, node_owner)

Where "MyScene" is simply a default CubeMesh, saved as a separate scene.

The resulting PackedScene, when saved, copied to a new project and instantiated via the editor, includes not only the desired instanced scenes, but also an instance of the original unmodified MyScene. I assume because I am not correctly assigning ownership, but I have not been able to solve the problem.

Any help appreciated, thanks

Drewton8