On 2015 form line 71, TT miscalculated the amount of SStax withheld by assigning W2 forms for me and spouse to one of us. This was not user error. It was software.

If it were TT's error, there would have thousands of complaints from users. That has not happened.

I have the exact same complaint. All info was correctly added into the W-2 section of turbotax (I pulled up the 2015 version and reviewed). Perhaps there aren't thousands of complaints because the IRS is just getting to these returns.

Yep ... if you entered the wrong code in box 12 of the W-2 then you could get the same issue although it is far less common a mistake.    If you used code A instead of the correct code, that error may also have produced excess social security.

check your box 12 on each actual W-2 form in your tax file:   a code "A" or code "M" with a $$ amount may also affect your line 71 value.

I stand corrected. A W-2 was attributed to the wrong person which raised the SS taxes over the individual limit resulting in an "overpayment." Those wiley cats over at the IRS caught the mistake. Explains why I had my first and only refund in 15 years of paying taxes...

Glad you figured it out.

Always review the prior year return side by side with the current year return to see the differences (especially if the bottom line is not what you expected ) and this error would have stuck out like a sore thumb.   Check the 2016 return as well to see if you duplicated the error especially if you transferred in the 2015 info to the 2016 return.

Thank you everyone who responded.  Turbo Tax asked me questions as I input the data (Any more W2's for you?  Any more W2's for your wife?) and the information was entered properly, as it had been done for the 17 years prior.  I am responsible for these delinquent taxes, but hey should own and admit their mistake...perhaps offer to pay the interest.

I have been using Turbo Tax since 1998 and have never had this issue.  If line 71 is a red flag for the IRS, why isn't this a red flag for Turbo Tax when they do their audit review?  "You've entered XXX on line 71.  Typically, this only applies if you or your spouse have multiple W2 forms."   This error could have been caught when tax forms were prepared in 2016, and I could have avoided the repeat error the following years.  I will take my business elsewhere next year.

@jlcurran

TTX does warn you about it....it pops up a page which shows you which spouse is assigned to the W-2 forms for-which the excess SS is "supposedly" going to be refunded, and gives you a chance to re-assign the W-2 forms to the appropriate person

.....  look at the pictures in the answers that  @Critter#2 showed below (on 1 October)

I just received my CP2000 notice from the IRS yesterday, July 16, 2018.  There are likely many others who will get their notice.  It's the same issue on line 71 and there was no pop-up warning.  All data was entered and assigned correctly - one W2 and employer for me with the data; then, one W2 and employer for my wife with the data.  

No error message was generated and I did not catch the line 71 excess SS calculation.  There were a few things that TT software asked me about during the final audit and before submitting my returns, but line 71 was not one of them.

I also checked my 2017 return, but there was/is nothing in line 71 for excess SS withdrawn.  I've used TT for years, but this screw up with their software is not acceptable.

@jstevenbaker

If you look at the answers below..you will see three expandable screenshots of the warnings that TTX presents the users....as soon as the excess occurs....after entering the offending W-2 form

The warning is there...sorry you missed it.

we seem to have this or a similar problem on our 2016 return with excess social security cited which now the IRS wants us to pay (and why didn't Turbo Tax say something to us at the time??) - It very much seems a Turbo Tax problem, and if it was entered by us manually incorrectly, then its fully valid to cite it as a desired 'enhancement' to the program to help ask 'Please confirm, did you use the correct code for this field? Turbo Taxes calculations show an uncommon situation where your social security withheld is over the allowed amount.'   

Once again that is a user entry error and you failed to read the warning screens. They have redesigned them 5 times in the past 5 years and somehow some users miss the warning every year  ...see the screenshot in the other answer to see the warning screen you miss read.

Again, I appreciate all of the responses.  I used Turbox Tax from the late 90's thru 2017.  The information is taken directly from the W2 forms for each person and there is NO POSSIBLE WAY for user error to combine just that one line.  The Turbo Tax screwed up by adding the lines together.  There was no warning because the program was messed up.  

I switched to H&R Block last year (2018) and could not bee happier.  No more Turbo Tax.  Good riddance.

I filed a claim with TT and of course the assessment came back that I requested to apply my wife's withheld social security to me.  Although I appreciate people taking time to explain that it was user error and that I got warnings and pop-ups, I truly don't recall getting those.  

Also, I find it impossible when completing the step-by-step process that I somehow reverted to applying my wife's W2 data into my line items.  The instructions in the tool are very clear - "Now let's complete Steve's employer data."  Then, - "Now let's work on [wife's name] employer data."  By the way, those things are imported and not even keyed in.  I know my employer vs my wife's employer.  That stuff is not complex or above my head.

The TT solution had my wife's name and employer identified.  But somehow I intentionally instructed the software to apply her employer to me and her line items?   I'm not buying it...even though I agree it's my fault that I did not scrutinize the output more closely.

I'm siding with the others who moved to H&R Block.  Somehow the TT programming crossed the wires.  But customers always have a voice for next time by voting with their feet.

Just FYI ... when you put in an accuracy claim the processor is able to open your account and is able to see exactly which entries you made, the computer made and  what was imported ( they are color coded).  So if the claim was denied then it must have been user entered.

Sorry ... this is 100% user error so get the error fixed for 2016 now before the IRS catches it and adds penalties & interest. 

You can try to put in an accuracy guarantee but don't expect a result in your favor ...

TurboTax has an Accuracy Guarantee for calculations by the program.  If there is a TurboTax calculation error the guarantee will pay any penalties or interest but not any taxes owed.  User errors are not covered by the guarantee.

See this TurboTax support FAQ for the Accuracy Guarantee -https://ttlc.intuit.com/questions/2566201-what-is-the-turbotax-100-accurate-calculation-guarantee

Open your 2015 return, and look at the worksheets. It will show you to whom you assigned each W-2.

I looked at each of the four W-2s worksheets and each item is correctly entered. Is there another form or worksheet where excess SS tax or tier 1 RRTA taxes might somehow come into play?

SweetieJean is right. The amounts were correct but the "to whom you assigned each W-2" was, in fact, the culprit. I stand corrected and am breaking out the ol' checkbook...

And the screens in the ONLINE version & the downloaded version are exactly the same so it is not the program.

The program screen for the warning has actually changed a bit every year to make the error easier for the user to understand but ultimately it is the user that has to read the warning and take action ... the program cannot do it for you.... see the 2016 screen here ...

see the 2014 screen here ...

and you should always review your return carefully before filing. If you had, you would have seen the SS overpayment there.

especially on a side by side comparison ... that should have stuck out like a sore thumb since you never had an amount on that line before...