Default IPv6 route metric changed from custom value to 1 after systemd network unit restart

Issue

System has default global GW specified as XXXX:YYYY::ZZZ in file /etc/sysconfig/network.

# cat /etc/sysconfig/network
NETWORKING_IPV6=yes
IPV6_DEFAULTGW=XXXX:YYYY::ZZZ
---8<---

#systemctl restart network

# ip -6 r show | grep default
default via XXXX:YYYY::ZZZ dev ethX metric 1 

The default GW metric was changed to some custom value along customer personal needs.
Lets take 2000 as an example here.

# route del -A inet6 default gw XXXX:YYYY::ZZZ dev ethX
or
# ip -6 route del ::/0 via XXXX:YYYY::ZZZdev ethX

# route add -A inet6 default gw XXXX:YYYY::ZZZ dev ethX metric 2000
or
# ip -6 route add ::/0 via XXXX:YYYY::ZZZdev ethX metric 2000

# ip -6 r show | grep default
default via XXXX:YYYY::ZZZ dev ethX metric 2000

There is again the default route with metric 1 after restarting of network service and the personal default GW route metric is lost.

#systemctl restart network

# ip -6 r show | grep def
default via XXXX:YYYY::ZZZ dev ethX metric 1