M:M Contact Address - two instances of the same address
We have configured the relationship between Contact and CUT Address as many to many, via S_CON_ADDR. The usage of the address is defined using the RELATION_TYPE_CD column in S_CON_ADDR - the address can be "Mailing" or it can be "Invoice".
An address of both types is required for a contact. This causes us problems where the customer wishes to use the same address for "Mailing" and "Invoice" purposes.
Technically, as the OOTB user key for S_CON_ADDR includes RELATION_TYPE_CD, it's perfectly possible to add two entries with the same CONTACT_ID and ADDR_PER_ID. For example: