Scrub Volume Command failed

I too have exactly the same problem.

root@ReadyNAS:~# btrfs scrub status /data
scrub status for c9439d9b-a5e6-47df-83fe-7988eedca356
scrub started at Thu May 29 10:06:56 2014, running for 6293 seconds
total bytes scrubbed: 384.43GiB with 0 errors
root@ReadyNAS:~# btrfs scrub cancel /data
ERROR: scrub cancel failed on /data: not running
root@ReadyNAS:~# btrfs scrub resume /data
ERROR: scrub is already running.
To cancel use 'btrfs scrub cancel /data'.
To see the status use 'btrfs scrub status [-d] /data'.
root@ReadyNAS:~# btrfs scrub start /data
ERROR: scrub is already running.
To cancel use 'btrfs scrub cancel /data'.
To see the status use 'btrfs scrub status [-d] /data'.
root@ReadyNAS:~#

Fact is, I know that the scrub actually finished. The log shows it finished a day ago.

My guess is that the scrub stat record file is incorrect/damaged/corrupt.
I understand there is an -f option on the btrfs scrub start to overcome a damaged stat record, but this option is not recognised on OS6.1.8.
Is there a way to force a scrub start?

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Update:
Found this http://bugzilla.kernel.org/show_bug.cgi?id=66151 which pretty much describes the problem.

Found the offending status file in /var/lib/btrfs.
Checked that no 'btrfs scan' task was running (htop).
(After backing up my data), I deleted the status file. That cleared the 'scrub in progress' status from frontview, and ran a new scrub.
After scrub finished ran 'cat' command on the status file to confirm all was okay.