I'm editing this post because now, after about the 10th install attempt, I think I am finally understanding this.
When the install completes, I am presented with the login page. The DE is set to "Default." After entering my password, the same screen is presented again. But if I switch DE to "MATE," then I can log in.
Please ignore my previous post about this.
(Note, however, that the message about the locking still shows.)