... but on further reflection, it looks like the IRS caused the problem. The IRS says only to include Line 72 of Schedule 5 on Line 6 of Form 2210. This prevents you from crediting estimated tax payments, and forces you to at least the Short Form of Form 2210, a nightmare. TT seems to have programmed the incorrect calculation which the IRS says to do. If Line 6 of Form 2210 allowed inclusion of estimated tax payments, there would be no problem. But the IRS form explicitly says to exclude them. This seems to be the crux of the problem.
