insserv problem with init.d script dependencies regarding 'mon'

[iam-TJ]

The following messages is repeated hundreds of times when installing/upgrading any package:

insserv: There is a loop at service mon if started
insserv: Starting usermin depends on mon and therefore on system facility `$all' which can not be true!

This is on Ubuntu 18.04 amd64 with usermin 1.760.

It seems like an impossible dependency between the services. It'd be preferable to add an option to install/use systemd service units for these.