Thank you, yes, my extension & payment is on schedule 3 line 10, and is shown on 1040 line 31, 1040 line 38 is blank :(
Understandably the estimated penalty that should have appeared on line 38 would have only been an estimate, but it would have been hell of a lot closer to the actual number than $0. This seems like a bug in the software, yet, this is something so simple to catch. If payer has extension AND taxes owed > taxed paid, calculate the interest owed. I'm just baffled I'm getting pinged to pay what is now an additional 1 month of interest.
