How to avoid the over ridding the supplier contact email address for the business classification

Customer has configured the Supplier Business Classification Expiration Notification, Customer is expecting to send expiry notification for the email id  mentioned in the addresses and sites, Other than the supplier contact email id.

There are 3 places that you can put an email addresses against a supplier.

Email address for the Purchasing site

Email address for the Remittances to be sent

Then you can also add a Contact for the Supplier and add that Contact’s email address.  When this email address is added to the system it over rides the other 2 email addresses.

Why does this happen and is there a way to stop this email address from overriding the other 2 email addresses?