Registering Picks with QOH, but no quantity available

We are using directed pick and putaway, no reservations or order tracking. However, the system appears to be "allocating" inventory based on the order in which the pick list was generated. We are a high volume, rapid turnaround manufacturing/distribution company and often have to allocate inventory or perform the actual shipments in a different order than the picks are created. When we go to register the pick, we often get a message that available inventory is negative even though there is adequate quantity in the bin. ](*,)

Can someone confirm that this is the way that NAV handles this (4.03SP), what tables are involved, and if they've modified this. We don't necessarily want to drive on hand inventory negative, but we do want to ship without having to cancel other picks, often with 30 plus items on them, to ship 1 item from an order. We are looking at modifying the code at this point.

Thank you so much.