Should localhost be managed by systemd-networkd?

I am moving from NetworkManager to systemd-networkd (after an upgrade to Ubuntu 18.04). I configured all my interfaces, bridges and VLANs and everything works.

The log shows that

root@srv ~# journalctl -b | grep " lo" | grep networkd
May 20 10:55:44 srv systemd-networkd[765]: lo: Removing non-existent address: ::1/128 (valid forever), ignoring
May 20 10:55:44 srv systemd-networkd[765]: lo: Link is not managed by us
May 20 10:55:44 srv systemd-networkd[765]: lo: Link is not managed by us
May 20 10:55:44 srv systemd-networkd[765]: lo: Link is not managed by us
May 20 10:55:44 srv systemd-networkd-wait-online[801]: ignoring: lo
May 20 10:55:44 srv systemd-networkd-wait-online[801]: ignoring: lo
May 20 10:55:44 srv systemd-networkd[765]: lo: Link is not managed by us
May 20 10:55:44 srv systemd-networkd-wait-online[801]: ignoring: lo
May 20 10:55:44 srv systemd-networkd-wait-online[801]: ignoring: lo
May 20 10:55:44 srv systemd-networkd-wait-online[801]: ignoring: lo
May 20 10:55:44 srv systemd-networkd-wait-online[801]: ignoring: lo
May 20 10:55:44 srv systemd-networkd-wait-online[801]: ignoring: lo

(ignoring: lo is then repeated many times down the log)

First of all, lo: Link is not managed by us. It is managed by whom, then?

Then it looks like it is somehow set up correctly:

root@srv ~# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever

It is indeed not managed by systemd-networkd:

root@srv ~# networkctl status lo
● 1: lo
       Link File: /lib/systemd/network/99-default.link
    Network File: n/a
            Type: loopback
           State: carrier (unmanaged)
         Address: 127.0.0.1

But otherwise works as expected:

root@srv ~# ping localhost
PING localhost (127.0.0.1) 56(84) bytes of data.
64 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=0.056 ms

Should I configure it via systemd-networkd and if so – how?