My son was using TT Deluxe, acquired on-line but accessible from his computer. I think it's "on-line" because I had a much harder time selecting forms from the return to print from his computer than with my copy of TT, that I had installed from the cloud -- purchased from Costco.
I discovered the issue: By entering an (low) incorrect "prior depreciation" amount, the program seemed to generate additional depreciation for the current year, but labeled it misleadingly as something to do with AMT. (Screenshot available upon request.)
(Fortunately, the property is owned equally by two domestic partners; we prepare both returns. The partner's return bore no irregularity. Tracing the differences led to discovery of our error. (I'm still puzzled why the error led to TurboTax generating some form of AMT adjustment!) (It doesn't hurt to have a retired EA for a father!)
BTW I found
Correcting the "prior depreciation" entry resolves the issue..
