A BOM has got several lines, one or more with negative quantity. Assumed, there is nothing on hand and a sales order for this BOM exists. Then Master scheduling creates a planned production order but it doesn’t calculate the negative lines as receipt.
MRP is calculating demands. Negative lines have no demand, no need to cover something. It doesn’t matter if the BOM line type is Item, Phantom, Pegged supply (AX2012) / Production (earlier versions), or Vendor.