FTP Backup to time-stamped subdirectory -- not deleting old backups

I have a scheduled backup to FTP, where a new time-stamped subdirectory is created and one backup file per domain is saved in it. It works great except I also have it set to delete backups older than 3 days and it does not (subdirectory + file contents still exist for many previous days). Furthermore, the email sent upon completion says this:
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Deleting backups older than 3 days ..
.. no backups to delete were found

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