Comment # 4 on bug 1102128 from Dr. Werner Fink

I do not get the problem.  If systemctl is called *afer* all configurations
(e.g. at boot) are done then it works ... is this correct?  In other words,
even if the configurations in /etc/sysctl.conf can be written as the sysctl
files

  /proc/sys/net/ipv6/conf/all/disable_ipv6
  /proc/sys/net/ipv6/conf/default/disable_ipv6
  /proc/sys/net/ipv6/conf/lo/disable_ipv6

those files will be set by e.g. wicked and/or NetworkManager and/or
systemd-networkd *after* systemd-sysctl.service had been called.

IMHO this has nothing todo with sysctl nor procps ...