Bug in Child and Dependent Care Credit with FSA

I have $5000 FSA and paid $12,579 for child care. I'm expecting that I can claim child care credit from the expense 12579 - 5000 = 7579, but TurboTax says:

"Since your $12,579 in care expenses wasn't enough to use up the $5,000 you contributed to your employer's dependent care plan, your Child and Dependent Care Credit is $0."
 
Isn't this a bug? How could $12579 "wasn't enough", as it's a larger number than 5000?