[BUG] beamer export -- text inside section, before next headline, has no frame [9.5.2 (9.5.2-ge7ea95 @ /home/hugo/.config/emacs/straight/build/org/)]

[Hugo Heagren <hugo@heagren.com>]

Remember to cover the basics, that is, what you expected to happen and
what in fact did happen.  You don't know how to make a good
report?  See

     https://orgmode.org/manual/Feedback.html#Feedback

Your bug report will be posted to the Org mailing list.
---------------------------------------------------------------------
---

I have org-beamer-frame-level set to 2, so when exporting to beamer,
top-level headlines become sections, and second-level headlines become
frames. I often want to include a short explanation/intro of the
section, before moving onto the more specific slide (I have found this
is good for complex lectures).

So I have something like:

```org
* A section
This is in the section, but not in the subsection (and is therefore
not in a frame, and shows up at the top of the slide).

** A subsection
Some text in the subsection. This /is/ in a frame, and so behaves
correctly.
```

As the MWE says, the text inside the top-level (section) headline, but
before the next (frame) headline, is not wrapped in a frame environment
when exported, so it renders strangely (at the top of the slide).

I feel like this is an easy fix for someone who understands the
exporter
code well. I've had a look and it's very complex, but I would be
grateful if someone else could try.

emacs  : GNU Emacs 29.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version
3.24.5, cairo version 1.16.0)
 of 2022-01-15
Package: Org mode version 9.5.2 (9.5.2-ge7ea95 @
/home/hugo/.config/emacs/straight/build/org/)

Blue skies, Hugo

Appendix.
---------

I tested the above MWE with the following minimal init.el and
reproduced the bug (well, it's minimal for me, since I'm used to using
straight and use-package, and didn't want to learn any other way of
installing all this stuff just to check a bug):

```elisp
(defvar bootstrap-version)
(let ((bootstrap-file
       (expand-file-name "straight/repos/straight.el/bootstrap.el"
user-emacs-directory))
      (bootstrap-version 5))
  (unless (file-exists-p bootstrap-file)
    (with-current-buffer
        (url-retrieve-synchronously
         "
https://raw.githubusercontent.com/raxod502/straight.el/develop/install.el
"
         'silent 'inhibit-cookies)
      (goto-char (point-max))
      (eval-print-last-sexp)))
  (load bootstrap-file nil 'nomessage))

;; Always integrate straight.el with use-package
(setq straight-use-package-by-default t)

;; Actually INSTALL use-package
(straight-use-package 'use-package)

(use-package org
  :straight (:includes ox-beamer))

(use-package ox-beamer
  :after org
  :config
  (add-to-list 'org-latex-classes
               `("beamer"
		 ,(concat "\\documentclass[presentation]{beamer}\n"
                          "[DEFAULT-PACKAGES]"
                          "[PACKAGES]"
                          "[EXTRA]\n")
		 ("\\section{%s}" . "\\section*{%s}")
		 ("\\subsection{%s}" . "\\subsection*{%s}")
		 ("\\subsubsection{%s}" . "\\subsubsection*{%s}")))
  :custom
  (org-beamer-frame-level 2))
```