Subcat list: linking to post retains subcat list

My site (WP 2.0) is a collection of family stories:
https://www.cousinagamfhein.net

The sidebar shows three categories (which are WP categories): Stories, Storytellers, and Characters.

The STORIES link produces a page with excerpts from all the stories on the site. That’s what it’s supposed to do. No problem there.

Both STORYTELLERS and CHARACTERS produce a list of their respective subcategories: names of people.

In the STORYTELLER category, the subcats are the names of the people who told the story (“told by Firstname Lastname”; in CHARACTERS, the subcats are the names of people who appear in stories (“Lastname, Firstname”).

In both cases, each name in the list is a link. If you clicked such a name, the site produced a list of all the stories associated with that name.

For example, if you clicked STORYTELLERS and then “told by Frank Macdonald,” you got all the stories for which he’s the storyteller. If you clicked CHARACTERS and then “Macdonald, Frank” yo got all the stories in which he appears as a characer.

Yesterday (May 2) I made what I thought were small changes: I replaced the default
the_category(, )
with
the_category( • )

Yesterday, when I clicked a name in either the STORYTELLERS or CHARACTERS list, I got:

(a) a list of the subcats under CHARACTERS, followed by
(b) the story excerpts matching the original choice.

In other words, if I click STORYTELLERS/told by Frank Macdonald, I get a list of all the characters in all the stories on the site, followed by the stories Frank told.

if I click CHARACTERS/Macdonald Frank, I still get a list of all the characters in all the stories on the site, followed by the stories in which Frank appears.

It’s obvious that some small change has caused this subcategory list (names of characters) to appear ahead of the stories — it DID NOT used to do this. What’s less obvious is the fix.

I have looked for a typo but have had no luck finding it. I also retrieved a backup version of all the theme files from a week ago, and used them to overwrite the ones on the site.

No help!

Any ideas for further investigation?