Routing disposition and credit lines

Hello. I have created a receipt route with 2 steps, and all disposition steps are non-payable. The items are payable at first step, and are on hand in stock at second step. If I recieve items in my route at first step, then voucher match, then do a disposition, I will get a credit line in my original PO, but I also get an automatic OV for the credit. Thing is if I recieve the credit line type C in my PO, the amount will be doubled. Is this some kind of bug? or an error in AAI configuration? Guidance