Payment Journal , Exhange rate problem

Hi all,

I post the invoice in USD and iam receiving the money in NOK .I have defined the Exchange rate for currency- NOK for 21/03/2010 and 23/03/2010 and In the payment if I manually change the exchange rate ( more or less rate compared with exchange rate setup ) and post the payment journal on 23/03/2010 .system still takes the exchange rate from the currency Exchange rates ?
The same functionality is working for Purchase Invoices / Sales Invoices means what ever exchage rate i enter in the purchase invoice / Sales invoice documents system posting invoice against that exchange rate only . It is not working for Payment journal .

Please let me know the problem.

Hi All,

Please throw some light about this.

Thanks in advance.