VFRB Retro Billing missing PDIF condition in L2 document

Hi All,

My issue is as follows.

Out Sales order having 2 batches in delivery document.

Billing document created with 2 line items as per batch, with same material and pricing, all the same.

1) while creating the retro billing  thru VFRB, system is creating  L2 document with PDIF condition determining for line item 10.

2) where as for line item 20 not PDIF condition added.

what could be the reason.

Please need your inputs.

thanks.