Artifacts
Backing up multiple artifacts (giving comma separated values without using all) is not supported right now. But, this can be achieved with a custom script with all the individual/specific backup commands.
This issue is fixed and will be working from release-0.89 onwards.Please refer documentation Configure backup
Postgres
Backing up and restoring a single db(eg openerp or openelis) is not supported right now.This can be achieved using the old way of backup and restore i.e. by creating a db dump.