[BUG] unfolding headlines with :extend face keyword & background broke after 2da622cad [9.7 (9.7-??-8ac99c33f @ /home/st/.config/emacs/.local/straight/build-30.0.50/org/)]

[StrawberryTea]

Hi, using the following test case with Emacs -Q:

(let ((default-directory (file-name-directory load-file-name)))
  (when (file-exists-p (expand-file-name "default.el" default-directory))
    (load-file (expand-file-name "default.el" default-directory))))

(straight-use-package 'org)

(require 'org)
(load-theme 'leuven t)

(dolist (face '(org-level-1 org-level-2 org-level-3 org-level-4 org-level-5
                org-level-6 org-level-7 org-level-8))
  (set-face-attribute face nil :extend t))

(setq org-fontify-whole-heading-line t)
(setq org-startup-folded t)

(defvar org-extend-faces-bug-4-file "/tmp/org-extend-faces-bug-4.org"
  "The file to be used for the bug demo.")

(with-temp-buffer
  (insert "* foo\n** bar\ntest\n** baz\ntest")
  (write-file org-extend-faces-bug-4-file))

(find-file org-extend-faces-bug-4-file)

The most recent fix for the bug in 2da622cad seems to have made things
worse. Now sometimes the background of the headline is not extended and
other times we still have the trailing background color where it's not
supposed to. It's definitely a lot worse when the file is started up
folded because the issue seems to be specifically related with unfolding
a heading with subheadings.

StrawberryTea <

Emacs  : GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo 
version 1.18.0)
 of 2024-03-04
Package: Org mode version 9.7 (9.7-??-8ac99c33f @ 
/home/st/.config/emacs/.local/straight/build-30.0.50/org/)