Oct 2019: I received a small refund from the IRS. I updated Turbo Tax and the tax due changed. Was there an error in Turbo Tax or did the IRS change something?

It is possible that from the time you filed and the time you just updated the program there was a program correction ... hopefully  you didn't make any changes by accident (if you did undo them) and you have a paper copy or PDF of the filed return you can use to review the current return to see what is different.  

FYI ... after you file you should never update the program before you have saved a PDF & .taxfile  to a removable storage medium ... only then should you run a program update. 

Did you have an underpayment penalty on 1040 line 23?  That was only an estimate.  Even if Turbo Tax calculates a penalty on line 23 it is just an estimate.  It's common and expected for the IRS to send a bill for more or even send a refund.  It is determined by when the IRS actually gets your tax due payment which Turbo Tax won't know.

Or If you filed early and had Schedule D for investments or sales in your return the IRS had an update and has been sending refunds or tax due bills.

IRS info on Schedule D changes (after May 15, 2019)

https://www.irs.gov/forms-pubs/error-in-tax-calculation-in-schedule-d-tax-worksheet-form-1040

I know that Turbo Tax was updated. What I want to know is what changed - was it an error in Turbo Tax or in tax tables provided by the IRS?  

This is exactly what happened. Thank you!

I meant to add it was the Schedule D issue that was the cause of the additional refund.

When did you file your taxes in October please? I did mine on the 14th and accepted, but as of today, still saying processing.

The discussion above has only to do with tax returns files before May 16, 2019.  msmurdaugh, the discussion above does not apply to you since you filed well after that date.