File-based backup in OpenVZ 7 is broken, OpenVZ 7 is not production-ready right now

File-based backup in OpenVZ 6:
https://openvz.org/Ploop/Backup#File-based_backup

File-based backup in OpenVZ 7:
not possible at all, it is broken now.

how to reproduce:

using prlctl
============

"prlctl snapshot-mount" and "prlctl snapshot-umount" not implemented,
file-based backup in OpenVZ 7 using only prlctl is not possible now.

using ploop
===========

# prlctl create test1 --vmtype ct
# prlctl start test1
# prlctl snapshot test1
Creating the snapshot...
The snapshot with id {fa2ea866-ee08-45eb-9cf4-d5a629fc21d6} has been successfully created.

# man ploop
A snapshot can be mounted using ploop mount -u uuid command, see above.

# ploop mount -r -m /mnt -u {fa2ea866-ee08-45eb-9cf4-d5a629fc21d6} /vz/private/3df6f5a8-d36d-4a77-83d9-532545fe8566/root.hdd/DiskDescriptor.xml
Error in ploop_mount_image (ploop.c:2368): Image /vz/private/3df6f5a8-d36d-4a77-83d9-532545fe8566/root.hdd/root.hds already used by device /dev/ploop34699

"ploop mount" failed with error.

using vzctl
===========

# prlctl create test2 --vmtype ct
# prlctl start test2
# prlctl snapshot test2
Creating the snapshot...
The snapshot with id {6d71a540-e419-4687-b436-0abd5ca27eba} has been successfully created.

# vzctl snapshot-mount test2 --id {6d71a540-e419-4687-b436-0abd5ca27eba} --target /mnt

# vzctl snapshot-umount test2 --id {6d71a540-e419-4687-b436-0abd5ca27eba}
Umount snapshot {6d71a540-e419-4687-b436-0abd5ca27eba}
Error in ploop_umount_image (ploop.c:2503): Image /vz/private/857d88d0-21e6-4a8a-9e03-878fdfa9034e/root.hdd/root.hds is not mounted

"vzctl snapshot-umount" failed with error.

resume:
=======

File-based backup in OpenVZ 7 is not possible now.

OpenVZ 7 is broken, and not production-ready right now.

production use OS without backups is not possible.

question
========

it is possible to fix these bugs with file-based backups?

or fixing bugs in OpenVZ 7 is not possible, and if I need
file-based backups - I should only use production-ready OpenVZ 6 ?

OpenVZ developers, can you please answer ?