Only IBAN is required in supplier setup but upon approval the bank account number auto populates

Summary:

We are trying to edit certain supplier bank details and are experiencing an issue where there is an IBAN populated in the Account Number . What we want is just the IBAN in the IBAN field and nothing in Account Number . When we remove the Account number and Submit for approval, the approver can see that we are removing the Account Number. Once approved the Account Number field is populated with part of the IBAN number. Is this a setting in the backend somewhere and how do we switch it off? We do not want any account