For one item / warehouse (that we know of so far), the On Sales Order quantity listed on the Stock Status report and the quantity on the Open Sales Order Report by Item report do not match.
Actually a difference of 4300. Can't seem to find a reason. I have rebuilt the Sort / Index files, recalculating the balances, and run the Balance Inventory Quantity and Cost utility (no differences found). Hoping that someone will have some insight or ideas.