I don't think anyone's really talking about the literal math, the adding and subtracting. It's more about pulling and putting the right numbers in the right places.
Here's an illustration. Say you sell a security that shows $X,Y00,000 proceeds of which $X,000,000 is cost basis and $Y00,000 is capital gain. It's really important to make sure only the $Y00,000 gets included in any taxable number. The 'math' in question is that this amount should be taxable and this amount shouldn't be, and the checking is that it was correctly expressed to Turbotax.
Turbotax will not make mistakes regarding the business logic of the forms. It will correctly "add the value from line 19d on schedule XYZ" every time. But Turbotax can't know that you entered the data correctly in the first place. It has no underlying concept of "this $Y00,000 shouldn't be taxed" or that you should have used schedule UVW instead of XYZ. It's just a fancy flowchart shuffling some spreadsheet cells. This is why you want to double-check Turbotax's operations using the form views that it provides. The form views are Turbotax's step-through debugger. If you think Turbotax is getting something wrong, it's much more likely that you misunderstood a question and entered something that wasn't what it was asking for.
Perceived bugs in Turbotax are right about in the same space as "blame the compiler" bugs in programming. They can exist, and poor messaging can create false positives, but 99% of the time, it's the user providing some kind of bad input instead.