Same problem for me. I'm helping my daughter with her taxes. She is married. She is our dependent. They are filing separately. On his 1040 box 12a ("Someone can claim...Your spouse as a dependent") needs to be checked however when doing so Turbotax gives an error on Smart Check "Married filing joint box should be selected since you indicated your spouse can be claimed as dependent of another person". Unless I'm mistaken this is a bug and not me misunderstanding the tax laws.
