TurboTax is following the tax law. That's the way it works. You can see the calculation on Form 8959. You might want to look at the IRS Instructions for Form 8959.
The additional tax from Form 8959 line 18 goes to Schedule 2 line 11. It's included in the total additional tax on Schedule 2 line 21, which goes to Form 1040 line 23 and gets included in your total tax.
But note Part V of Form 8959, which calculates your total Additional Medicare Tax withholding. That additional withholding, from line 24, goes to Form 1040 line 25c and is added to your other withholding, so it partially offsets the additional tax.