Wierd partition behaviour with BTRFS

[Patrick O'Callaghan]

(Sorry for the subject line but it's the best I could come up with)

I recently installed F20 on a new system with a 120GB SSD and 1TB hard
drive. I'm using the SSD for /, /boot, /var and swap, and the hard drive
for /home. I decided to live on the edge and partition /home as BTRFS.
All this was done from Anaconda with no subsequent changes except adding
a few labels.

This is what I find:

$ lsblk --fs
NAME   FSTYPE LABEL                                                     UUID                                 MOUNTPOINT
sda                                                                                                          
├─sda1 ext4   boot                                                      6d5929d8-fd35-49e6-a8bf-aab5309dad77 /boot
├─sda2 btrfs  fedora_pxeclient-arch-00000-undi-002001-d4-3d-7e-f4-1b-08 22fecad3-619d-4a9b-aace-35a2e4e04c49 /home
├─sda3 ext4   root                                                      6a9a800c-309b-4b69-b269-884ad495e7b9 /
├─sda4                                                                                                       
├─sda5 ext4   var                                                       d5955869-af07-4d6e-b1b3-6ccb31208b41 /var
└─sda6 swap                                                             1431e6d2-531e-46cd-8633-1cf878c6b2a1 [SWAP]
sdb                                                                                                          
└─sdb1 btrfs  fedora_pxeclient-arch-00000-undi-002001-d4-3d-7e-f4-1b-08 22fecad3-619d-4a9b-aace-35a2e4e04c49 

Note that /dev/sda2 and /dev/sdb1 have the same UUID and label.

$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda3              68G  8.5G   56G  14% /
devtmpfs              7.8G     0  7.8G   0% /dev
tmpfs                 7.9G  5.6M  7.8G   1% /dev/shm
tmpfs                 7.9G  1.1M  7.9G   1% /run
tmpfs                 7.9G     0  7.9G   0% /sys/fs/cgroup
tmpfs                 7.9G   72K  7.9G   1% /tmp
/dev/sda1             477M  113M  335M  26% /boot
/dev/sda5              27G  1.8G   24G   7% /var
/dev/sda2             932G   73G  858G   8% /home

Note that /dev/sda2 is mounted and /dev/sdb1 is not. However /dev/sda2
has around 1TB of space, so it's clearly the hard drive.

What's going on, and should I be worried?

Also, how can I change the label of the BTRFS partition? I used the
"btrfs filesystem label ..." command but although it registers the
change, the existing fedora_pxeclient.... label still shows up
in /dev/disk/by-label.

poc