I am using openerp 7 and trying to purchase a product from my supplier. The product expense account is type of expense while the supplier payable account is type of payable account.

I confirmed a purchase order and try to pay the invoice from the PO. However the amount shown is negative. Is the negative amount here is normal ? Because I notice in odoo 10 when I make a payment of vendor bills, the value shown is positive.

What did I do wrong ?