LPC Not calculating Previous invoices until make the payment

Hi Gurus,

I am encountering a issue, scenario is

I have 4 Months outstandings

ex: January month....Rs.100

      February month..Rs.100

      March................RS.100

      April..................Rs.100

In order to Month end activity,If i tried to run February interest through FPINTM1 transaction code, its not calculating LPC for previous invoices but if the consumer made the payment in June month its calculating LPC in next invoice (Including previous all invoices ). I am not understating how system is behavior.

Suggest me why it is not calculating LPC every month previous invoices?

Thanks,

ABBAS