unRaid 6.2: cache disks (double BTRFS) cannot unmount

After upgrading to 6.2 from 6.1.9 array-stop cannot unmount my cache-disks. I run with dual-BTRFS setup. It seems the array-disks are dismounted just fine, but the cache disks are reported as busy. 'sudo lsof | grep mnt' shows nothing, neither does fuser /mnt/cache.

I have reverted to 6.1.9 and it unmounts again. I have no rush to upgrade, so I'll hang in there.

I did a scrub (and a balance) after downgrading to 6.1.9 and it did not report any problems.

I have attached syslog. These lines might be interesting:

Oct  2 14:49:15 Tower emhttp: shcmd (33): mkdir -p /mnt/cache

Oct  2 14:49:15 Tower avahi-daemon[1823]: Server startup complete. Host name is Tower.local. Local service cookie is 464192456.

Oct  2 14:49:15 Tower emhttp: shcmd (34): set -o pipefail ; mount -t btrfs -o noatime,nodiratime -U eac59635-6227-4f2b-a3d0-7559b8970403 /mnt/cache |& logger

Oct  2 14:49:15 Tower kernel: BTRFS info (device sde1): disk space caching is enabled

Oct  2 14:49:15 Tower kernel: BTRFS: has skinny extents

Oct  2 14:49:15 Tower kernel: BTRFS: detected SSD devices, enabling SSD mode

Oct  2 14:49:16 Tower emhttp: shcmd (51): set -o pipefail ; /usr/local/sbin/mount_image '/mnt/cache/app/docker/docker.img' /var/lib/docker 15 |& logger

Oct  2 14:58:24 Tower emhttp: shcmd (102): set -o pipefail ; /usr/local/sbin/mount_image '/mnt/cache/app/docker/docker.img' /var/lib/docker 15 |& logger

Oct  2 14:58:24 Tower root: /mnt/cache/app/docker/docker.img is in-use, cannot mount

Oct  2 14:58:24 Tower emhttp: err: shcmd: shcmd (102): exit status: 1

Docker didn't seem to be running: /etc/rc.d/rc.docker stop exitted quickly and there were no docker process 'ps -ef | grep docker'.

Best Alex

syslog.2016.10.zip