Failed to sync: source and parameter to --backup-dir mustn't overlap

Thanks ncw.
The following is a more detailed description of the issue.

Here is the filter_rules file, where “.spacemacs” is a file:

+ /home/wolfv/.spacemacs
+ /DATA/**
+ *

Source is / (root)
DATA is a different partition mounted on root.
Destination is a USB drive mounted on root.
I created a local remote named “local”, and put the USB drive on it:

 local:/run/media/wolfv/big_stick/wolfv_backup

I added --one-file-system to the rclone command but still get the same “–backup-dir mustn’t overlap” error:

$ rclone sync / /run/media/wolfv/big_stick/wolfv_backup/last_snapshot --backup-dir=local:/run/media/wolfv/big_stick/wolfv_backup/old_files --suffix=_2018-06-28_09:17:59 --filter-from=/DATA/Documents/pc_maintenance/backup_systems/rclone_wolf/filter_rules --log-level=DEBUG --one-file-system --dry-run
2018/06/28 10:53:52 DEBUG : rclone: Version "v1.41" starting with parameters ["rclone" "sync" "/" "/run/media/wolfv/big_stick/wolfv_backup/last_snapshot" "--backup-dir=local:/run/media/wolfv/big_stick/wolfv_backup/old_files" "--suffix=_2018-06-28_09:17:59" "--filter-from=/DATA/Documents/pc_maintenance/backup_systems/rclone_wolf/filter_rules" "--log-level=DEBUG" "--one-file-system" "--dry-run"]
2018/06/28 10:53:52 DEBUG : Using config file from "/home/wolfv/.config/rclone/rclone.conf"
2018/06/28 10:53:52 INFO  : Local file system at /run/media/wolfv/big_stick/wolfv_backup/last_snapshot: Modify window is 1ns
2018/06/28 10:53:52 ERROR : Fatal error received - not attempting retries
2018/06/28 10:53:52 Failed to sync: source and parameter to --backup-dir mustn't overlap

This is similar to Sync two partitions with one rclone command? but with the addition of --one-file-system and --backup-dir=local:/run/media/wolfv/big_stick/wolfv_backup/old_files
(I apologize for double posting, I originally thought they were two separate issues).

Once the “–backup-dir mustn’t overlap” error is resolved, there is still the matter of --one-file-system flag:
--one-file-system is needed to fix “–backup-dir mustn’t overlap” error.
--one-file-system breaks access to the /DATA partition, as it did in Sync two partitions with one rclone command?
Do you see a way out of this conundrum?