Pricing calculation requirement when use retro billing

Dear All ,

Our client requirement is for retro active billing ,

But i have some issue in that after executing the VFRB ,

E.g. Earlier the rate was 160 Rs. , after some time  new rate was amended which is 170 Rs.,

now i have to generate the debit note for customer for the difference value of 10Rs.

I had execute the VFRB , the debit note was generated  , but in that debit note i have found that ,

1) Net value displayed is not calculated as per the difference value  i.e. 10 Rs. ,

2) In condition tab the  condition PDIF condition shows the correct calculation , but the still net value is incorrect ,

Kindly help to know  how  will be calculation when using the retro billing , ?

Regards,

Sourabh