Gaurav,
Yes it is standard behavior , Couple of check points
Check which version is used in Valuation variant?
If you work without costing versions, the exchange rate type is determined through the valuation variant (CO version 'T Code-OKEQ' in the valuation strategy for internal activities). if you use Costing versions then it enable you to specify that another exchange rate type has priority (T-Code-OKYD).
Thanks
Hrusikesh