pfSense

In addition, static mappings are currently being added without the prefix, even when a prefix is available.

Details here: https://forum.netgate.com/topic/197470/kea-dhcpv6-bug-with-early-dns-registration-for-tracked-interfaces/

Seems like the bug could be around here in https://github.com/pfsense/pfsense/blob/master/src/etc/inc/system.inc

foreach ($dhcpifconf['staticmap'] as $host) {
$ipaddrv6 = $host['ipaddrv6'];

if (!$ipaddrv6 || !$host['hostname']) {
continue;
}

• We are always in an "end-user" subnet
• here, which all are /64 for IPv6.
  */
  $prefix6 = 64;
  } else {
  $prefix6 = get_interface_subnetv6($dhcpif);
  }
  $ipaddrv6 = merge_ipv6_delegated_prefix(get_interface_ipv6($dhcpif), $ipaddrv6, $prefix6);

There probably should be some sort of guard, like:

$ifaddrv6 = get_interface_ipv6($dhcpif);

if ($isdelegated && !is_ipaddrv6($ifaddrv6)) {
continue;
}

$ipaddrv6 = merge_ipv6_delegated_prefix($ifaddrv6, $ipaddrv6, 64);

if (!is_ipaddrv6($ipaddrv6) || Net_IPv6::isInNetmask($ipaddrv6, '::', 64)) {
continue;
}