It's unlikely that this feature of TurboTax has a problem. I'm sure it has something to do with your entries.
I just now tested a joint tax return with $24,000 of wages in box 1 of my W-2, $2,000 with code D in box 12 and entered a Form 1099-R reporting a Roth conversion of $25,000, producing an AGI of $49,000. When I go through the Retirement Savings Contributions Credit section and indicate that I am not a full-time student, that I cannot be claimed as a dependent and the neither I nor my spouse received any distributions that were not rolled over over or converted to Roth, TurboTax produced the correct $200 credit on Form 8880.
I'm assuming that the $49,000 of income that you stated is your AGI and included the taxable amount of the Roth conversion. It's your AGI that determines the credit ratio.
