Payment Format Validation - Document Payee Bank Number is not working as expected

Hi,

I have setup a payment validation at Payment Format level:

Document Payee Bank Number is Required for Payment Method: Electronic

I have then created a payment and for one invoice of a Supplier setup with a Bank Account Number this validation failed.

The only thing that I can think of is that I am displaying only the last 2 numbers in the Supplier Bank Account (I am using the Supplier Mask functionality).

Any ideas why the application can be behaving like this?

Thanks,

cv