Line 4b of the Form 1040 is based on the what you entered on the Form 1099-R box 2a and checked the box for IRA/SEP/SIMPLE.
Go back and review the Form 1099-R you entered.
To enter, edit or delete a form 1099-R -
Click on Federal Taxes (Personal using Home and Business)
Click on Wages and Income (Personal Income using Home and Business)
Click on I'll choose what I work on (if shown)
Scroll down to Retirement Plans and Social Security
On IRA, 401(k), Pension Plan Withdrawals (1099-R), click the start or update button
As DoninGA implies, if you enter Forms 1099-R correctly TurboTax produces the correct result on Form 1040 line 4b. After entering the Form 1099-R and answering the questions that immediately follow, you must also click the Continue button on the page that lists the Forms 1099-R and answer any questions that apply to your Forms 1099-R in aggregate.
In what way is the amount on Form 1040 line 4b different from what you expect?
What is the code in box 7 of the Form 1099-R that you received for the distribution that you expect to be reported (or not reported) on Form 1040 lines 4a and 4b? Is the IRA/SEP/SIMPLE box marked?