Changing the type of a node that has been transformed into ROOT deletes all nodes

[rogeriodec]

Godot version:
3.1

OS/device including version:
Windows 10 x64 / NVIDIA GeForce GTX 1060 6GB / Intel Core i7 4790K

Issue description:
Changing the type of a node that has been transformed into ROOT deletes all nodes

Steps to reproduce:

1. Create a new scene / 3D scene
   
2. Create a new node
   
3. Right click on the new node and click on "Make Scene Root"
   
4. Right click on the new root node and click on "Change Type" (choose for example, "Spatial")
   
5. All children nodes disappear
   
6. And also you can't undo
   

[Zylann]

Similar to #27222

[Zireael07]

But not an exact dupe, I believe?

[groud]

Yes, closing as a duplicate of #27222

[follower]

Based on my investigations it seems this issue wasn't an exact duplicate of #27222 because it seems while this issue no longer occurs in a semi-recent nightly build, the issue described in #27222 does still occur.