foreman=# SELECT id,identifier,mac,attrs,created_at FROM nics WHERE host_id = 690 AND identifier = 'br_tun' ORDER BY identifier;
id | identifier | mac | attrs | created_at
--------+------------+-------------------+---------------------------------------------------------+----------------------------
125 | br_tun | 92:60:6f:d8:23:4c | --- !ruby/hash:ActiveSupport::HashWithIndifferentAccess+| 2015-03-31 21:45:41.582826 | | | mtu: '1500' +| | | | |
220002 | br_tun | ea:e5:ed:bd:a8:4a | --- !ruby/hash:ActiveSupport::HashWithIndifferentAccess+| 2015-11-10 20:52:03.44866 | | | mtu: '1500' +| | | | lldp_neighbor_portdesc: '' +| | | | lldp_neighbor_portid: '' +| | | | lldp_neighbor_sysname: '' +| | | | lldp_neighbor_mngaddr_ipv4: '' +| | | | lldp_neighbor_mngaddr_ipv6: '' +| | | | lldp_neighbor_pvid: '' +| | | | lldp_neighbor_mtu: '' +| | | | |
(2 rows)

foreman=#

example bad data

host = Host::Managed.find(690)
macaddress_br_tun_fact_name = FactName.where(name: 'macaddress_br_tun').first
macaddress_br_tun_fact_value = FactValue.where(fact_name_id: macaddress_br_tun_fact_name, host_id: host).first
macaddress_br_tun_fact_value.value = 'aa:aa:aa:aa:aa:a1'
macaddress_br_tun_fact_value.save

host.populate_fields_from_facts

Test case to reproduce.