You said line 4a is larger than 4a (the same line number). I assume you meant that 4b is larger than 4a.
It's not a mistake. TurboTax is attempting to follow the somewhat confusing and ambiguous IRS instructions for lines 4a and 4b. If all of your IRA distributions are fully taxable, the amount is added only to line 4b, not line 4a. Similarly, if all of your pension distributions are fully taxable, the amount is added only to line 4b, not line 4a. If you have partially taxable IRA distributions and fully taxable pension distributions, or vice versa, you end up with line 4b larger than 4a. The IRS instructions made sense in past years, when IRAs and pensions were on separate lines, but they cause confusion when IRAs and pensions are combined on one line, but the instructions still treat them separately.
Take a look at some of the other threads re: this problem.
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