Unable to make fields Mandatory in Customer Bank account page

Unable to make fields Mandatory in Customer Bank account page

Navigation:

Receivables--> Billing--> Manage Customers--> Account Number-->Payment Details-->Payment Instruments-->Bank Accounts

the edit bank account page opens in a separate window and unable to customize.

Hence, we have modified in the same screen - Bank accounts page . however it is showing as mandatory but still it accepts null values without any validation. We believe both are of different pages