btrfs filesystem contents disappeared after reboot

Running a multi disk RAID 1 with btrfs for a while now on a Virtual Lab Server with Ubuntu 14.04 amd64.
Today, after a clean reboot due to power failure initiated by the NUTS Daemon, when the system came back online, the filesystem of this specific RAID 1 disappeared.

df -h shows very little disk space used in the RAID 1:
    /dev/sdb 597G 80M 595G 1% /kvm

ls -las /kvm shows no files:
    total 4
    4 drwxr-xr-x 1 root root 0 Apr 21 11:26 .
    0 drwxr-xr-x 1 root root 186 Apr 14 00:35 ..

btrfs filesystem show /kvm shows that apparently the previous information is still in the hard drives:
    Label: none uuid: 45075b5b-a389-445a-b70e-00a1bfcd313a
            Total devices 2 FS bytes used 39.68MiB
            devid 1 size 298.09GiB used 158.03GiB path /dev/sda
            devid 2 size 298.09GiB used 158.03GiB path /dev/sdb
Btrfs v3.12

No subvolumes or snapshots exist, since no output is given from btrfs subvolume list /kvm

Running a scrub on the RAID 1 completes successfully, with no errors found, but only processes approximatle 80Mb of files:
    scrub status for 45075b5b-a389-445a-b70e-00a1bfcd313a
            scrub started at Mon Apr 21 15:37:55 2014 and finished after 1 seconds
            total bytes scrubbed: 79.36MiB with 0 errors

Running a FS Check on both hard drives reveals no errors:
    Checking filesystem on /dev/sda
    UUID: 45075b5b-a389-445a-b70e-00a1bfcd313a
    checking extents
    checking free space cache
    checking fs roots
    checking csums
    checking root refs
    found 4382862 bytes used err is 0
    total csum bytes: 0
    total tree bytes: 188416
    total fs tree bytes: 8192
    total extent tree bytes: 36864
    btree space waste bytes: 57988
    file data blocks allocated: 41418752
     referenced 41418752
    Btrfs v3.12

    Checking filesystem on /dev/sdb
    UUID: 45075b5b-a389-445a-b70e-00a1bfcd313a
    checking extents
    checking free space cache
    checking fs roots
    checking csums
    checking root refs
    found 4382862 bytes used err is 0
    total csum bytes: 0
    total tree bytes: 188416
    total fs tree bytes: 8192
    total extent tree bytes: 36864
    btree space waste bytes: 57988
    file data blocks allocated: 41418752
     referenced 41418752
    Btrfs v3.12

Tried to perform a restore on one of the hard drives, but no information was recovered.

Would really appreciate some feedback on this one, could be a really serious btrfs bug.

Kind regards,

Márcio Santos

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: btrfs-tools 3.12-1
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
ApportVersion: 2.14.1-0ubuntu3
Architecture: amd64
Date: Mon Apr 21 15:29:28 2014
SourcePackage: btrfs-tools
UpgradeStatus: Upgraded to trusty on 2014-03-21 (30 days ago)