I understand what you're saying.  However I don't believe it affects 2020, but your point would affect 2021.  Therefore it needs to be fixed.

Let's assume 1 stockholder. The Federal deduction is the actual $17,000 resident tax paid.  The Maryland deduction - there is none. We add back the $17,000 to the Federal income on the K-1's so the K-1 recipient reports the proper MD income on their own tax return. And as the full $17,000 passes to the K-1 recipient, 2020 has no issue.

This is the same as nonresident tax. It matters not what you paid, you get benefit for the greater of what you paid or the actual tax due.

But to your point, if the correct tax to have been paid was $7,760 and the 510 form shows $6,400 then next year when (if, like we do on individuals) we have to report the overpayment as a Federal income addition we cannot go by the $6,400 as shown on the 510. So I believe you are correct and we need to notify ProSeries @Orlando help!