Bursting control file pick up the wrong value from the XML output , why?

In R12.2, the bursting control, base one the filter ( also a variable from XML output ), can be either PRINT or EMAIL.  My problem is that when the invoice is set to PRINT ( the filter is working ), it get the P_XXX_COPIES from previous <xapi: request> which is NULL.  That cause the bursting control program failed.

Here is the example of the bursting control .  Also attach the sample of the xml output. 

In the XML output, the first invoice #10000 is P_XXX_DELIVERYMETHOD=EMAIL,  P_XXX_COPIES=NULL, P_XXX_VALUE=fushan@AAA.com.   I checked and the email send out successful