With Collaborative Editing enabled, all users are sharing the same draft. However, if a single user wants to leave the editor and discard his own changes, he doesn't have the option to do so unless:
- He manually removes his changes.
- He clicks on the 'Undo' button in the page until his changes are gone.
At present, he can only either remove everyone's changes or keep everyone's changes along with his own. Also, when you "Save and Close" Undo button will not remember the previous action, thus, Undo button will not disregard the changes.
Provide an extra button or option ("Discard my changes") whereby the user can discard his own changes.