The `kamctl start|stop|restart` is provided as a basic non-unix/linux-standard way to start stop kamailio. It should not be mixed with other start/stop systems such as init.d or systemd.
While you encounter the issue on an OS using systemd, there are other OSes still using init.d or maybe even other start/stop systems. Kamailio can also be started by hand from terminal, like running just `kamailio` or with cli parameters `kamailio -f /etc/kamailio/kamailio.cfg -w /run/kamailio -m 128 -M 12 ...`
I think it will be rather complex for kamctl to figure out how kamailio was started (or how it was supposed to be started on that OS) in order have all start/stop variants working all the time.
If someone wants to undertake such task, he/she is welcome to make a pull request.