Open Amount in requisition

Hi,

We have a situation wherein business is creating the Requisition(Order type OR) through Outside Operation and post approval they are generating Purchase Order(Order type OS) through that requisition. But sometimes they change the supplier as well as the unit cost while generating the Purchase Order and then they receive the same. This leaves some open amount against requisition when inquired through Open Requisition Enquiry(P4310) while open quantity is fine i.e. zero as full quantity is received in Purchase Order. Due to this issue work order can not be closed since there is open amount in the related Requisition. Hence every