Some settings are not visible in frontmatter although present in files

I’m using the default Quark theme. I set up body classes using the Normal mode "Body classes" field and verified that it worked fine for my page.

However, when I switched Admin UI to Expert mode, I was surprised to see `body_classes` missing from the frontmatter editor. I thought that maybe it was stored somewhere entirely else, but then I opened up the page md file in a text editor and I saw that body_classes is present there.

I refreshed the admin UI multiple times - the same result, no `body_classes` in frontmatter but present in both file and UI Normal mode "Body classes" form field.

What’s going on? Why does Grav admin UI not display `body_classes` in the frontmatter when it’s present in the file?

I was under impression that frontmatter should include everything I set in the Normal mode dialogs. Otherwise I'm in a strange situation when I can actually configure more things through UI than frontmatter.

Reproduce the behavior in the Grav Admin UI by setting Body classes in Normal mode, switching to Expert mode, and comparing the editor with the saved page markdown file. Trace how the body_classes setting is represented in both views; done means the visibility behavior is explained and the frontmatter editor consistently reflects the saved setting.

Written by the indexing model from the issue text.