Description
When using the undo in Prefab Mode, autosave can become confused. If this happens the user is stuck in the prefab editing window. The only way to exit is via the task manager or force quit.

Steps to reproduce.
- Open the linked project
- Open the Character Creation Scene
- Open the Animation Window.
- Move animation to different frame (make sure it is set on preview mode)
- Try to modify prefab
- Notice: Prefab is not saved and cannot get out of prefab mode
(once animation window preview mode is set to false, it is possible to get out)

VIDEO ATTACHED

Project files: https://oc.unity3d.com/index.php/s/l3I4QcnAl1mgP8P