[question] behavior after rollback

Case:
have progressive snapshots dating years.

I rollback to 1 month ago.
btrbk starts and makes a new snapshot today.

How will the snapshot be taken and sent to backups?
1) using the one from 1 month ago as parent
2) using the last one from the old branch as parent without problems
3) using the last one from the old branch as parent causing problems and breaking progressive backups
4) will somehow recognize that we are in a new branch and do some magic
5) something else

Thanks in advance, and would be great to have the answer also on the README, Restore Backup section :)