Thanks for all your help, guys.
(sigh)
There's a saying, "You learn something new every day." Unfortunately, I seem to be learning the same things over and over. In
this post I noted my solution to the original problem. Turns out that was the solution this time, too.
In my defense, I had the EPUBs of another series that I had processed successfully and they did NOT have the "calibre:title_sort" field changed. I guess I must have changed them within calibre and forgotten that the field in the OPF and the calibre title sort field were the same thing. (shrugs)
Kovid, why is the sort field used instead of the title? I really would like to understand how all this stuff works.
Are the ASIN and and ISBN significant as bernie suggests? I had already removed them, so it is just another "Oh, by the way" things.
Thanks, again.