Item Allocation from Debrief number while debrief status is unprocessed

Dear Guru's

We are on R12.

Kindly need your inputs regarding the major requirement of the customer that, when we entered the item in debrief and the status of debrief is unprocessed, the item which is required in Debrief must get allocate/reserve against this debrief number. Right now I checked in inventory there is no allocation is been made while status is unprocessed, its get directly issued from store when debief status change to complete. which we don't want that. first it must reserve and after that issue.

The reason is may be at the same time one can request the item for 2 debrief lines(different SO).