Why is the checkbox on line 7 of form 1040 blank? Schedule D is not attached and it is not required for my return. The numeric field for line 7 is blank.

Everything appears to be calculated correctly throughout the return.  This question is just about whether or not the checkbox should have been selected by TurboTax.  The exact instructions on form 1040 are "Attach Schedule D if required. If not required, check here" so it seems like a mistake to neither have Schedule D nor to have the checkbox selected.