Btrfs devel - Feb 2014 - Frequent error messages (block group X has wrong amount of free space)

I've recently installed ArchLinux on a Lenovo Ideapad laptop.
Right on the first day of use, I received error messages at boot time
like these:

BTRFS error (device dm-0): block group 11840520192 has wrong amount of
free space
BTRFS error (device dm-0): failed to load free space cache for block
group 11840520192


Then I added the clear_cache option to see if the problem would go
away. After 3 boots, it did go away. But after some more boots, it's
back!

I believe there has been no unclean shutdowns nor lock-ups so far.

What could be causing this error during normal operation?

I have:
Kernel 3.12.9
btrfs-progs 3.12

/etc/fstab:

# /dev/mapper/luks-pool
UUID=c56031b3-af27-41f6-8103-ede1f0743ac0       /               btrfs
         subvol=arch,compress=zlib,nospace_cache,rw,noatime,clear_cache
 0 0

# /dev/mapper/luks-pool
UUID=c56031b3-af27-41f6-8103-ede1f0743ac0       /var            btrfs
        
subvol=arch-var,compress=lzo,nospace_cache,commit=180,rw,noatime,clear_cache
   0 0

# /dev/mapper/luks-pool
UUID=c56031b3-af27-41f6-8103-ede1f0743ac0       /home           btrfs
         subvol=home,compress=zlib,nospace_cache,rw,noatime,clear_cache
 0 0


Thanks!
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