IPv6 only interfaces missing from sys.hardware_addresses and sys.hardware_mac

root@dev ~ $ 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
2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 02:e2:37:e7:21:68 brd ff:ff:ff:ff:ff:ff
    inet 10.0.2.15/24 brd 10.0.2.255 scope global dynamic enp0s3
       valid_lft 85521sec preferred_lft 85521sec
    inet6 fe80::e2:37ff:fee7:2168/64 scope link
       valid_lft forever preferred_lft forever
3: enp0s8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 08:00:27:2b:f3:ae brd ff:ff:ff:ff:ff:ff
    inet 192.168.100.10/24 brd 192.168.100.255 scope global enp0s8
       valid_lft forever preferred_lft forever
    inet6 fe80::a00:27ff:fe2b:f3ae/64 scope link
       valid_lft forever preferred_lft forever
4: enp0s9: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 08:00:27:72:69:2c brd ff:ff:ff:ff:ff:ff
    inet6 fde4:8dba:82e1::c4/64 scope global
       valid_lft forever preferred_lft forever
    inet6 fe80::a00:27ff:fe72:692c/64 scope link
       valid_lft forever preferred_lft forever
root@dev ~ $ cf-promises --show-vars | grep "fde4:8dba:82e1::c4"
default:cfe_autorun_inventory_ip_addresses.ipv6_addresses  {"fde4:8dba:82e1::c4","fe80::a00:27ff:fe2b:f3ae","fe80::a00:27ff:fe72:692c","fe80::e2:37ff:fee7:2168"} source=promise  
default:sys.ip_addresses                  {"127.0.0.1","10.0.2.15","192.168.100.10","fe80::e2:37ff:fee7:2168","fe80::a00:27ff:fe2b:f3ae","fe80::a00:27ff:fe72:692c","fde4:8dba:82e1::c4"} source=agent
root@dev ~ $ cf-promises --show-vars | grep "08:00:27:72:69:2c"
root@dev ~ $ cf-promises --show-vars | grep "sys.hardware"
default:host_info_report_inventory.inventory_vars {"default:cfe_autorun_inventory_dmidecode.total_physical_memory_MB":"","default:cfe_autorun_inventory_ip_addresses.ipv4[10.0.2.15]":"10.0.2.15","default:cfe_autorun_inventory_ip_addresses.ipv4[192.168.100.10]":"192.168.100.10","default:cfe_autorun_inventory_listening_ports.ports":["22","53","5308"],"default:inventory_any.id":"bootstrap","default:inventory_os.description":"ubuntu_18 (LSB missing)","default:sys.arch":"x86_64","default:sys.cf_version":"3.15.0a.cf9e38064","default:sys.class":"linux","default:sys.cpus":"4","default:sys.flavor":"ubuntu_18","default:sys.fqhost":"dev","default:sys.hardware_addresses":["02:e2:37:e7:21:68","08:00:27:2b:f3:ae"],"default:sys.host":"dev","default:sys.interfaces":["enp0s3","enp0s8","enp0s9"],"default:sys.ipv4":"10.0.2.15","default:sys.key_digest":"MD5=7ee138d9968c85e4255cd9283a6489a2","default:sys.os_release":{"BUG_REPORT_URL":"https://bugs.launchpad.net/ubuntu/","HOME_URL":"https://www.ubuntu.com/","ID":"ubuntu","ID_LIKE":"debian","NAME":"Ubuntu","PRETTY_NAME":"Ubuntu 18.04.3 LTS","PRIVACY_POLICY_URL":"https://www.ubuntu.com/legal/terms-and-policies/privacy-policy","SUPPORT_URL":"https://help.ubuntu.com/","UBUNTU_CODENAME":"bionic","VERSION":"18.04.3 LTS (Bionic Beaver)","VERSION_CODENAME":"bionic","VERSION_ID":"18.04"},"default:sys.release":"4.15.0-62-generic","default:sys.uptime":"16","default:sys.uqhost":"dev"} source=promise
default:sys.hardware_addresses            {"02:e2:37:e7:21:68","08:00:27:2b:f3:ae"}                   inventory,source=agent,attribute_name=MAC addresses
default:sys.hardware_flags                {"up loopback running","up broadcast running multicast","up broadcast running multicast"} source=agent
default:sys.hardware_mac[enp0s3]         02:e2:37:e7:21:68                                            source=agent
default:sys.hardware_mac[enp0s8]         08:00:27:2b:f3:ae                                            source=agent
root@dev ~ $