AI_ADDRCONFIG dropping loopback in IPv6 only network with IPv4 loopback

[skrivy]

Testing environment:

• Network configuration:

root@test:~# 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
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
48: eth0@if49: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 00:16:3e:62:e8:9f brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet6 2001:db8::1/64 scope global mngtmpaddr dynamic
       valid_lft 86103sec preferred_lft 14103sec
    inet6 fe80::216:3eff:fe62:e89f/64 scope link
       valid_lft forever preferred_lft forever

• Memcached listening on IPv4 loopback:

root@test:~# lsof -n -i -P | grep 11211
memcached 8655 memcache   26u  IPv4 18850563      0t0  TCP 127.0.0.1:11211 (LISTEN)

• Memcached is working properly - telnet 127.0.0.1 11211 with commands work fine

Test script:

#!/usr/bin/perl

use Cache::Memcached::Fast;

my $memcached = Cache::Memcached::Fast->new({
        'servers'            => [ '127.0.0.1:11211' ],
});

# Ensure we can actually talk to the memcached server
my $ismemcached = $memcached->set('ismemcached','1');
unless ($ismemcached) {
    warn "\nNOT WORKING\n";
}

However, when I reconfigure memcached to listen on IPv6 as well and update the code:

-        'servers'            => [ '127.0.0.1:11211' ],
+        'servers'            => [ '::1:11211' ],

Everything works as expected.

Culprit:

https://github.com/JRaspass/Cache-Memcached-Fast/blob/master/src/connect.c#L44

Is there any reason to set AI_ADDRCONFIG flag in this library?