I believe your interpretation to be fair, however, it seems illogical to me that the taxpayer should have to pay a penalty for paying their taxes (for 2021) late because they chose not to defer (in 2020.)  Either Proseries agrees or they have an error in the software (it wouldn't be the first time!)  Either way I am going to fight this and I am going to have to answer about 75 IRS notices on this issue.  How do I get an explanation from Proseries as to their error, or a statement from them if they believe there was no error in the calculation?