Enter prior year Roth IRA contributions

On the "Enter Prior Year Roth IRA Contributions" page, there is a field labeled "Roth IRA contributions prior to 2021."  TurboTax has always been accurate in the amount that it shows in this box.  It has always been the sum of all previous years' contributions.  All contributions have been the result of conversions from an IRA.  There is a note, "Do not include earnings and losses or amounts converted from a traditional IRA," though that seems to have had no effect on the amounts, which TurboTax automatically enters into the box.  (I have been using TurboTax since before the creation of Roth IRAs.)

 

This year, however, the amount in the box is less than the amount that was in the box last year.  This year's amount is the result of this calculation:  Roth IRA contributions prior to 20

20

minus Roth IRA distributions taken in 2020.  I would have expected this year's amount to be the result of this calculation:  Roth IRA contributions prior to 20

21

minus distributions taken in 2020.

 

While this amount has no impact on my tax liability, I don't understand how TurboTax arrived at this amount.  Has anyone else had this kind or problem?  Am I misunderstanding these numbers?  Is there a change in how this amount is calculated, or is this a defect?