Payment block defaulting to D in vendor master

Hi all,

I have a vendor master where in the initial payment block was "D" and when I try to remove the payment block and save, it gets saved,but when the vendor master is opened, pyament block D is defaulted again.

In other words, every time I remove the payment block in vendor master, it is saved with blank payment block but whenI reopen the vendor, payment block D is  getting defaulted.There are no open items to the vendor.

Below attached is the chagne log of hte vendor master.

Best regards,

Prakash.