From my tests on , I can confirm the following behavior:
1. Administrator user edits the page https://localserver/xwiki/bin/edit/Sandbox/TestPage1 (either through in-place editing or WYSIWYG editor), adding a modification, keeping the page editing open

2. User B tries to edit the same page and sees the message that the pages is blocked in editing by another user.

3. User B forces the editing session of the page, adds a modification, saves and closes their session

4. Administrator user saves and closes the editing of the page on their side and it added both their modification and the one of User B.

5. Administrator user edits the page again and has the editing session still open.

Potential problems:
6. User B tries again to edit the page, the message to force the editing session is not shown again, being given the option to edit the page directly, both editing sessions (of Administrator user and User B) are active

Then, adding a third user in the scenario:
7. While have the 2 editing sessions described above still open (the last editor opening an editing session being User B), User C tries to edit the same TestPage1 and sees the "This page is currently locked by Administrator" message, even if the last user that opened an editing session on the page is User B.

Positive aspect: the saved modifications of all users from their simultaneous editing sessions are merged into one version.
Negative aspect: not having the message shown each time a user tries to edit a page that is still open in edit mode by another user could cause confusion.

The main Q here is, why is the "This page is currently locked by ..." not displayed a second time?