Section's baseof template overriden by theme baseof

I’ve filed this asa bug here: https://github.com/spf13/hugo/issues/2995

What’s happening

(also see img below)

This happens on both Hugo 0.18.1 and Hugo 0.19-DEV. Didn’t happen on Hugo 0.18-DEV

I have a theme, with default layouts defined as follows: ./themes/freja/layouts/_default/{baseof,list,single}.html

For the gen section of the website I’ve overriden all of them:
./themes/freja/layouts/gen/{baseof,list,single}.html

And now the section’s baseof template isn’t used.

Screenshot of the file tree:

./themes/freja/layouts/_default/baseof.html is a regular html file:

<!DOCTYPE html>
<html lang="{{.Site.LanguageCode}}">
...
<body>
<main>
  {{ block "main" . }}
  {{ end }}
</main>
</body>
</html>

whereas ./themes/freja/layouts/gen/baseof.html is just a shell:

{{ block "main" . }}

{{ end }}

The rest of the templates are quite similar.

The result for /gen should look like this: https://dmitriid.com/gen/social/ Now, however, the output is surrounded by HTML from the theme’s default baseof.html

I wonder what changed, or ami I doing something wrong?

Please remember that, by double posting this, you make me handle the same issue twice.