Unit List Price and Price List not appearing in P&A form after 1st order creation

Dear All

I have a customized version of P&A form in which when I click Price & Availability button Unit Selling Price, Unit List Price and Price List get populated in their respective fields. I click create order button and order is created. I want to enter another order and and this time when I click Price & Availability button Unit List Price and Price List do not populate in their respective fields. Every time  have to close form and reopen it then it works fine. I want to know from which source Unit Selling Price, Unit List Price and Price List get populated. There is something wrong in code which I need to correct. In which code should I look?? Or at least the statements where code assign values to