Storage plugin leaves extra '@' subdirectory after second and subsequent migration

I’ve noticed that the storage plugin seems to perform the first migration (from eMMC to external device) correctly, but that after a subsequent migration (from external device to another device), an extra ‘@’ subdirectory is left just below ‘/srv’. This is in addition to the BTRFS sub-volume ‘@’ at the device root, as shown in the examples below.


First migration

Foris notification after reboot:

Your /srv was successfully moved from /dev/mmcblk0p1 to /dev/sdb1

Console session:

root@turris:~# df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/mmcblk0p1            7.3G    524.1M      6.8G   7% /
tmpfs                   503.3M    480.0K    502.8M   0% /tmp
tmpfs                   512.0K         0    512.0K   0% /dev
/dev/sdb1                14.3G     16.5M     12.3G   0% /srv
root@turris:~# mount -o ro /dev/sdb1 /mnt
root@turris:~# find /mnt -type d
/mnt
/mnt/@
root@turris:~# find /srv -type d
/srv
root@turris:~# 

Second migration

Foris notification after reboot:

Your /srv was successfully moved from /dev/sdb1 to /dev/sda2

Console session:

root@turris:~# df -h
Filesystem                Size      Used Available Use% Mounted on
/dev/mmcblk0p1            7.3G    524.1M      6.8G   7% /
tmpfs                   503.3M    524.0K    502.8M   0% /tmp
tmpfs                   512.0K         0    512.0K   0% /dev
/dev/sda2               112.0G     16.4M    110.9G   0% /srv
root@turris:~# mount -o ro /dev/sda2 /mnt
root@turris:~# find /mnt -type d
/mnt
/mnt/@
/mnt/@/@
root@turris:~# find /srv -type d
/srv
/srv/@
root@turris:~#