Yes, your first example demonstrates a bug. That appears to be a new page in online TurboTax for this year. The desktop version of TurboTax does not appear to have that page and does the calculations correctly.
I suspect that if the online version did not block the entry of proper spousal contributions, the underlying tax forms would be prepared correctly.
TurboTax developers seem to be adding a bunch of buggy fluff to the online version this year.
