application of the IAS 21 (The Effects of Changes in Foreign Exchange Rates) on oracle payables.

application of the IAS 21 (The Effects of Changes in Foreign Exchange Rates) on oracle payables.
we have the following case:
invoice currency: EUR
invoice amount: 481,706.73 EUR
rate exchange: 1EUR=102.225710 DZD
invoice date :12/10/2010
Functional money :DZD
converted amount :49,242,812.49 DZD

at 31/12/2010 we should update the converted amount with the closing rate:
31/12/2010 exchange rate: 1EUR=99.572678 DZD
the converted amount should be: 47,964,829.11 DZD
and we should account an exchange gain: 1,277,983.38 DZD

the payment of this invoice was at 05/01/2011
05/01/2010 exchange rate : 1EUR=97.740433 DZD
if we pay this invoice with the payment forms we should have an exchange gain: 2,160,588.12 DZD
but in this case the exchange gain should be : 882,604.75 DZD