"corrupt 1", but no other indicators

I'm seeing the following message on every bootup in dmesg & /var/log/messages:
BTRFS: bdev /dev/sda2 errs: wr 0, rd 0, flush 0, corrupt 1, gen 0

I've tried running scrub and it doesn't indicate any errors occurred Is this normal? Is something actually corrupted? Can I fix it?

Details:

[root@mireille ~]# uname -a
Linux mireille.svist.net 3.19.1-201.fc21.x86_64 #1 SMP Wed Mar 18 04:29:24 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux [root@mireille ~]# btrfs fi show
Label: none uuid: 5ac56e7d-3d04-4ffa-8160-5a47f46c2939
Total devices 1 FS bytes used 237.28GiB
devid 1 size 465.76GiB used 465.76GiB path /dev/sda2

Btrfs v3.18.1
[root@mireille ~]# btrfs --version
Btrfs v3.18.1
[root@mireille ~]# btrfs fi show
Label: none uuid: 5ac56e7d-3d04-4ffa-8160-5a47f46c2939
Total devices 1 FS bytes used 237.28GiB
devid 1 size 465.76GiB used 465.76GiB path /dev/sda2

Btrfs v3.18.1
[root@mireille ~]# btrfs fi df /
Data, single: total=457.75GiB, used=232.64GiB System, single: total=4.00MiB, used=80.00KiB Metadata, single: total=8.01GiB, used=4.64GiB GlobalReserve, single: total=512.00MiB, used=0.00B

dmesg: http://pastebin.com/9B0h4SuA

It's a cumulative counter, so it's harmless. The problem has already been automatically fixed. You can reset the counter with btrfs dev stats -z.

Chris Murphy