Sorry, I was away from my system,
This seem to be issue in your planner profile
Accounting®Financial Accounting®Special PurposeLedger®Planning>Define Planner Profile.
When defining the planner profile, you can set an indicator for the second and third currencies, so that entries can be made in these fields. This allows you to make entries in these currencies without the amounts in the first currency being translated to the second and third currencies.
If this indicator is not set, the amounts in the first currency are automatically translated into the second and third currencies, if you have included these fields in your planning.
Please refer to following for more information
http://help.sap.com/saphelp_46c/helpdata/en/fd/18d7b6604511d39716006094b969cf/content.htm
http://help.sap.com/saphelp_erp60_sp/helpdata/en/da/6ada3889432f48e10000000a114084/frameset.htm
http://scn.sap.com/message/8822392
Thanks,
Nishan Dev