OK ... so you are using a calculator/estimator and not the acutal program. The estimator works the same way just with a different path ... when you entered the $15K expense the program gave you a credit based on the $6K max allowed then when you entered the $5K the credit was naturally reduced which reduced the refund. This is normal. You got the tax reduction when you put the money into the FSA ... you saved fed/SS/medicare taxes on that $5K which is better then simply a % credit on the tax return.
