Just for the record, in MAAS 1.9 we have code in interface.py (the node network interface model object) which handles a pre-delete signal for network interfaces, and uses it to delete_related_ip_addresses(). There is no such code in MAAS 1.8 for MAC addresses, which is why this is a problem on MAAS 1.8 but not 1.9.
Just for the record, in MAAS 1.9 we have code in interface.py (the node network interface model object) which handles a pre-delete signal for network interfaces, and uses it to delete_ related_ ip_addresses( ). There is no such code in MAAS 1.8 for MAC addresses, which is why this is a problem on MAAS 1.8 but not 1.9.