… so what’s correct way then, when system command which reboots system is not the one?
for another round of science I’ve done another reinstall, verified that everything is 2.5M2
then i’ve stopped zram with sudo service zram-config stop
unfortunately there was nothing to umount as /var/lib/openhab2 was not mountpoint anywhere
and then rebooted
and after logging back 2.4 again 
I know I’m just blindly rebooting system, but I would like to know how this should be done then