IRS credited my estimated taxes twice! How does this happen with TT?

[Clockwork-12]

I just got a letter from IRS saying:

"We changed your 2021 form 1040 to match our record of your estimated tax payments, credits, applied from another year, and/or payments received with an extension to file. As a result you are due a refund of $3658."

This amount was paid in October 2021 as a estimated pre-payment tax.  I used TT Business sIRS, TT and my calculations show total tax due for 2021 was $7685.  IRS says I paid them $11,343.  They added $3658 twice ($37 from a 1099, $3658 from estimated tax payment, $3658 from schedule 3 which does not exist in my 1040 forms, and $3990).

The AGI and TI match exactly. Tax due match. They say there was estimated tax payment from form 1040 line 26 Sch 3 line 10 for $3658.  I didn't submit this form. It was not part of the TT documents. My estimated prepayment was entered on line 25d of the 1040.

How do they (IRS)  add a schedule 3 form and credit estimated prepayment amount twice?

[RobertB4444]

@Clockwork-12  It sounds like the IRS made a math error in your favor.  You should expect that they will correct it on their own and hold on to whatever increased refund you will have to return to them when they ask.  Keep it in an interest bearing account.

[Clockwork-12]

That is what I thought too. I worked so hard to get the numbers exact on TT and then to have received this letter.  I find it interesting that someone, I presume, physically goes through the 1040 and reviews it and decides that I made an error and sends me money.  I would have thought that the computers do the analysis and by using TT, each line item would be accurate. Makes me wonder how many more people received such a refund....