A/R Invoice that link with Down Payment document have reversed GST from DP

Question

Hi All,
I am buzzle on why SAP has changed their function for down payment in 8.81 version. For example, if SO amount is $1000 and GST is $70, but company request their customer to pay $500 as deposit (add GST $35). In SAP 8.81 version, the double entries will be as below:
Down Payment Invoice
Dr Customer                        $535
Cr GST                                         $  35
Cr Down Payment Clearing Acct $500
Incoming Payment
Dr Bank                              $535
Cr Customer                               $535
Invoice (final)
Dr Customer                                 $535
Dr Down Payment Clearing Acct $500
Cr GST                                                 $70
Dr GST                                          $35
Cr Sales                                              $1000
In the final invoice, why there is a reversal of GST amount from Down Payment invoice? In previous version, final invoice will only calculate the GST amount base on balance amount instead of currently credit with full sales amount's gst and reverse previously posted gst amount from down payment invoice.
This will cause problem if down payment invoice and final invoice are few months apart. Company will have paid the down payment invoice's gst amount. Anyone knows the logic for current changes? Appreciate if anyone can help, thanks.

Answer 1

Dear Expert
Let me clarify my client's scenario more to see whether you could give advise.
My client's business is project based and the invoicing flow is as below:
Phase 1 -
Invoicing  30%
Phase 2 -
Invoicing  30%
Phase 3 -
Invoicing  40%
                                               Total 100%
However, invoice for phase 2 maybe issued before invoice for phase 1 is paid and so do invoice for phase 3.
There is also possibility that invoice for phase 1 is paid while invoice for phase 2 is not at the time when whole project is completed. Invoice for phase 3 therefore has to be issued before invoice for phase 2 is paid.
The installments for A/R is not applicable in this case since sales would be realized at the time when the A/R invoice is issued.
My client would have to realize the sales upon completion of project phase. A/R down payment invoice almost satisfy this scenario however, no A/R invoice of the balance with reference to the down payment invoices can be issued before the down payment invoices are settled.
Can anything be done to overcome this limitation?
Regards
Elton