The short answer is there was no error. I made a mistake in my assumption regarding the absence of taxes from my estimated income amounts.
I spent an hour manually doing the Estimated Taxes using the IRS forms. Came up with the same answer. So I am wrong and TurboTax was right!
The problem was that the calculations used for the estimated tax worksheet were not transparent, so there was no way for me to figure this out except by doing the calculations using the paper forms.
