I have created a field using studio in customer bank accounts called "Sort Code".  

(Vendor record, accounting tab)

(Click through to view bank accounts)

(Click through to the form view)

the problem i am having is when i go to payments. I went to a payment, and add a related field to the sort code. (partner_id.bank_ids.x_studio_sort_code).

If i change the Vendor Bank account field, the "sort code" field will not change. How can i set this up correctly so the correct sort code from the bank account line shows when another account number is selected?