Negative Sales Order Quantity not included in MRP Calculations

I have a "credit" order for an item using an exist order type.  For accounting purposes, instead of using actual credit orders, we simply enter a sales order with negative quantities.  So, the shipping plant shows a positive commitment and the purchase order shows a negative commitment.

I can see the items in the Supply / Demand screen.  However, these quantities seem to be ignored when MRP is run.  IN other words, we do not see the inventory will increase in the shipping branch with prompts to order sooner than we need; inventory will decrease in the shipping branch with prompts for expired inventory even though it won't be there.  The order type & status are included in the Supply/Demand inclusion rules (and you can see them when the orders are entered "normally").  I'm not sure if there is something in the setup that I've missed to