If there was no change to line 43, it's unlikely that there would be any change to line 44 if your tax was determined entirely from the tax table. Apparently your tax was determined using some other worksheet or form and the IRS made some change to one of values used in the calculation on that worksheet or form.
Also, the IRS isn't always right in determining these sorts of changes. You'll need to determine what they changed that caused the change in the amount on line 44 since it's extremely unlikely that the cause was an actual calculation error by TurboTax. The IRS calls any difference between the IRS's results (based on information provided directly to the IRS from various sources such as Forms W-2 and 1099) and your tax return a "calculation error." "Calculation error" does not necessarily imply a math error or even any error in processing the input you provided to TurboTax.
