W. tax calculation problem in case of down payment?

Hi,

I am making a down payment and system is calculating the amount as below:

1) Made a downpayment with special G/L indicator of Rs.500 and deducted TDS Rs50

2) Made an invoice of Rs.2000 and deducted TDS Rs 200, so Invoice is Rs.1800

3) Now, we have cleared the downpayment against this invoice number and system is showing the payment received 450 and invoice 1800 and no information in W.tax tax of F-44 for both. Which means if the we have to make a payment then we have to pay Rs. 1350 - 50 = 1300

4) Ideally, if we check the system should deduct Rs.1400 (2000-500-200), but after entering the payment in F-53 I have checked the system is asking for 1150 payment

Please clarify as I am unable to understand it...

Thanks in advance

Regards

Nitin