Vat Settlement

DEAR ALL

this is regards to Vat Settlement:- full scenario is as under

AS for the first time when i m poting vat Settlement i have the Follwing figures available

VAT INPUT 4000
VAT OUTPUT 1200
CST PAYABLE 2400

So it means thers should be Vat Carried Forward of Amount of Rs. 400

But When i POsting VAt Settlement system passes the following entry


PARTICULARS DEBIT CREDIT
CST Payable 1,200
VAT Payable 1,200
VAT Payable 4,000
VAT Input Receivable 4000
VAT Payable 2,800
VAT Payable 2,400
Vat Excess Carried Forward 400
CST Payable 2,400
VAT Payable 2,400

So After this entry My CST Payable Account Showing 1200 Debit Amount

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Vat Payable Acount Showing 1200 Credit Amount

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Vat Input is NIL

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And Excess Vat Carried Forward is 400

BUt i m confused in CST Payable and Vat Payable Account my confusion is that first of all i m not able to understand the entry that has been done by system moreover Both these account are showing some unexpected amount so if any one can clarify me on this Issue that will be highly appreciative
i m using Navision 4.0 SP3(HF2)

thanks
Jogi