I wrote out this post, then found the solution before I posted it. I’m posting it here in case someone else encounters the same problem.
In one of my projects, structure-based section type assignment is working just fine.
However, in my main project, it isn’t. No matter what type I assign to the various files and folders, everything is given the type “title page.” “Title page” shows up wherever I check it (outliner, inspector). It says “Structure-based from [name of root folder].” The root folder isn’t even assigned the type “Title page,” though. Nothing I change seems to make any of the section types change.
Is there any way I can reset this project somehow, so that it might work properly?
HOW I SOLVED THE PROBLEM: I erased the too-powerful section type (“Title page”) and everything was assigned its correct type. I then created a new “Title page” type without problems.