I am not sure if my procedure is incorrect or if there is a programming logic problem.
 
I use swap subtitute parts in the work order module quite often.  Usually, the item I am substituting is not on the swap substitute part list.  I get a message that asks if this is okay.  I answer yes.  Then in the quantity of the original material, I enter 0(zero).   The material in the work order shows only the substitute item.
 
However, when I run MRP, a planned order is generated for the part I am manufacturing for a customer order and for the orginal material even though I already have a work order in existence for that part.  
 
It is not a case of an additional order being placed by the customer.  There is only one requirement.
 
I don't believe this was happening before but I'm not sure, as I have not been using the MRP for long.  Anyone else having this problem or know a solution?

Not if the work order already exists - in that case it should be only looking at the WOBOM.  Let me see if I can duplicate what you describe, it could be a problem with the sap substitute program.

Then it is a problem because it shouldn't    Let me see why it is.  It should only be looking at the master BOM if the WO doesn't exist or if it is status S meaning it has no WOBOM.  We have MRP on the programming table this month, one more for the pile!