How is 2020 TT calculating 2021 Estimated Taxes? Seems Wrong

Is there a problem with the 2020 TT calculation for 2021 Estimated Tax Payments?  

Using the Estimated Tax Payment Options worksheet, I select the 4th box: 100/110% of 2020 tax.  TT calculates an amount that is neither 100/110% of 1040 line 24 Total Tax.  In fact it’s an amount that doesn’t fit any percent of line 24.

Looking back at 2019, I find that using the same worksheet and selecting the same option, TT does calculate correctly the 100/110% of 1040 line 16 Total Tax.  

How is 2020 TT calculating the Estimated Tax Payment amount?  I know I can override this number but usually overriding a TT calculated amount is not a good thing to do.  

I have installed the latest TT update so that’s not an issue.  

Anyone have an understanding of this or seeing the same problem?  (I’d advise you to check because I wouldn’t have normally and wouldn’t have seen it was wrong until filing 2021 and probably an IRS penalty for underpaying.)