What is happening is the client paid before the due date.  You listed the due date as the date the client will be paying.  Thus the IRS realized the client paid one month earlier than the date you listed.  Hence the refund of miscalculated tax penalty.  Always ask client when they will be paying if subject to penalty and enter on form.  If you go back and change on your computer to date paid you will find the difference.

Intuit always defaults to due date as date paid on form 2210.  You have to change to actual date paid!