Scene tree is cleared when switching tabs

[KoBeWi]

Godot version

2c7fcdd

System information

W10

Issue description

When you move to another scene tab, the tab you just left is cleared:

The nodes are visible on scene, but when you save it and reload, your scene will be lost.

Steps to reproduce

1. Add some child nodes to a scene
2. Switch to another scene tab
3. Return

Minimal reproduction project

No response

[akien-mga]

Tested a local revert on a hunch, this was caused by #55512 (@RandomShaper).

[akien-mga]

This also affects the 3.x branch as of 716580b due to the merge of #55514.

[RandomShaper]

I'm trying to fix it. If I don't see a chance to do it quickly, I'll let you know so you can revert.