Disk quota exceeded

[Matthew Jurgens <default.mailbox@edcint.co.nz>]

I've create a subvolume
CMD: btrfs quota enable /export/shared
CMD: btrfs subvol create /export/shared/TV/files
Create subvolume '/export/shared/TV/files'
CMD: btrfs quota rescan /export/shared/TV/files

I've assigned a small quota to it:
CMD: btrfs qgroup limit 100M /export/shared/TV/files

I've also disabled copy on write:
CMD: chattr -R -V +C /export/shared/TV/files
chattr 1.42.12 (29-Aug-2014)
Flags of /export/shared/TV/files set as ---------------C

CMD: sync; btrfs qgroup show -r /export/shared/TV/files
qgroupid         rfer         excl     max_rfer
--------         ----         ----     --------
0/5           2.11TiB      2.11TiB         none
0/1894       16.00KiB     16.00KiB    100.00MiB

I created one file until I exceeded the quota using:
CMD: dd if=/dev/zero of=/export/shared/TV/files/junk1 count=50 bs=1M
CMD: dd if=/dev/zero of=/export/shared/TV/files/junk1 count=50 bs=1M
dd: error writing ‘/export/shared/TV/files/junk1’: Disk quota exceeded
50+0 records in
49+0 records out
51380224 bytes (51 MB) copied, 0.0238218 s, 2.2 GB/s

then I removed the file
CMD: rm /export/shared/TV/files/junk1

I tried to create it again (and only got 900k written before the quota 
was exceeded):
CMD: dd if=/dev/zero of=/export/shared/TV/files/junk1 count=50 bs=1M
dd: error writing ‘/export/shared/TV/files/junk1’: Disk quota exceeded
1+0 records in
0+0 records out
917504 bytes (918 kB) copied, 0.000568984 s, 1.6 GB/s

then I removed the file
CMD: rm /export/shared/TV/files/junk1

I tried to create it again (and this time got 900k again written before 
the quota was exceeded):
dd if=/dev/zero of=/export/shared/TV/files/junk1 count=50 bs=1M
dd: error writing ‘/export/shared/TV/files/junk1’: Disk quota exceeded
1+0 records in
0+0 records out
917504 bytes (918 kB) copied, 0.000943652 s, 972 MB/s

The usage looks ok:
CMD: sync; btrfs qgroup show -r /export/shared/TV/files
qgroupid         rfer         excl     max_rfer
--------         ----         ----     --------
0/5           3.10TiB      3.10TiB         none
0/1894      912.00KiB    912.00KiB    100.00MiB

But I can not create any more files:
CMD: dd if=/dev/zero of=/export/shared/TV/files/junk1 count=50 bs=1M
dd: failed to open ‘/export/shared/TV/files/junk1’: Disk quota exceeded

CMD: lsattr /export/shared/TV/files
---------------C /export/shared/TV/files/junk1

During other tests I have managed to get it to the point where I can't 
delete the file (since disk quota exceeded).
I've waited many minutes to ensure commits etc. The only way I can 
seemingly consistently get the ability to write to the directory again 
is to reboot. Immediately after a reboot I can create files as expected.

It seems like copy on write is still functioning for this directory? or 
quota results have delays?
I've tried mounting the subvolume to another location, but same results.

Is this happening because quotas are not yet considered stable?
Is there something I am doing wrong?




Other Info:
The fstab entry:
LABEL=SHARED            /export/shared          btrfs 
defaults,compress=lzo,relatime,nofail 0 1

uname -a
Linux gw.lambert.rd.to 4.2.7-200.fc22.x86_64 #1 SMP Thu Dec 10 03:28:47 
UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

btrfs --version
btrfs-progs v4.2.2

btrfs fi show
Label: 'SHARED'  uuid: 199672d4-69ef-4ecf-865a-851bed0167d5
         Total devices 5 FS bytes used 3.10TiB
         devid    1 size 2.73TiB used 1.27TiB path /dev/sdc
         devid    2 size 2.73TiB used 1.27TiB path /dev/sdf
         devid    3 size 2.73TiB used 1.27TiB path /dev/sdh
         devid    4 size 2.73TiB used 1.27TiB path /dev/sde
         devid    5 size 2.73TiB used 1.27TiB path /dev/sdd

btrfs fi df /export/shared
Data, RAID10: total=3.16TiB, used=3.09TiB
System, RAID10: total=64.00MiB, used=352.00KiB
Metadata, RAID10: total=9.00GiB, used=7.61GiB
GlobalReserve, single: total=512.00MiB, used=0.00B

dmesg:
http://edcint.co.nz/tmp/dmesg_20151219.log