Automatically update bank account number when IBAN number is changed

Content (required):

Hi all, 

I have an issue I need to understand the logic behind. I have enabled internal supplier bank account changes approval on our test environment. The approval flow and routing are working fine for supplier bank account changes. However, I tried to change only the IBAN number for a customer from 'NO6381014384065' to 'NO6381014384065 - DLM' and when it was approved the bank account number for the same customer changed as well from '81014384065' to '438406'. I went into the audit report for this area as well. and from here I could see that the change in IBAN also changed the bank