Ouch!
Except . . . while I do make mistakes when I create new listings, that wasn't the case here. I used the List Similar, copied and pasted in the changes (title and 3 places in the description), got the new picture, and hit "Preview". I got an error message that I had to enter the weight for domestic shipping. The listing that I copied had Flat Price, somehow it got changed to Calculated. Because it had happened before, I knew enough to browse through the entire preview. That's when I found all the switches had been flipped, so I changed them before I submitted it. It never got listed with the errors, but I discovered the point at which they occurred.
It sounds like the bug is triggered by an error message, whether it's a new one or editing an existing one. And that doesn't explain why the switch got flipped for domestic shipping. I have entered thousands of listings using List Similar and this never happened before.