Edit a content.
Set the title to "Content v1"
Set the subtitle to "nothing"
Save
Edit the content
Set the subtitle to "my worthy subtitle"
Wait until it is save in draft

With another user:
Edit the content
Set the title to "Content v2"
Save

With the first user:
Edit the content
It will propose you to restore your unsave date
If you accept it will rollback the title to "v1" without warning you (but you will have the "worthy" subtitle)