Shop order close pulls the data for the finance transactions from where ?

We are using IFS 7.5 and we are closing a shop order. Very simple shop order, issues only from received PO’s sitting in project inventory, no material burden, no labor, no standard plan parts. Assume the value of the purchases is 100, the cost of the bacflushed items is 100, but when the shop order is received and closes the OOREC transaction shows a cost of 110. The system then creates a negative & positive entry (SOMTRLV- & SODIFF+)  to bring the cost back to 100 so in the end it self corrects. My question is where does the system get the cost of 110 from ? We had no unissuing, or unreceiving, or cost revaluations, and the costs of the components were the same when we received and closed the shop order as they were when we issued the component parts. To my knowledge we hadn’t fiddled around with the quantities of the components in the shop order. The system is finding an additional cost of 10 from somewhere, but I have no idea where.  What costs does the shop order close consider ? It’s only bothering me because the accounting transaction for the extra 10 failed to be caught by the accounting rules and ended up as an erroneous posting, and I want to know where it went wrong so we can fix it so it doesn’t happen again.