When a second user starts editing the same page as a another user,
the message that the other user is editing the page already is not shown.
It says only the second (=current) user started editing the page but it should display that the first user is editing also the page.

How to reproduce:

• start editing a page with a user (e.g. superuser)
• edit the same page with another user (e.g. eric)
• eric gets the notification "eric starts editing this page" – correct would be to pass that information to the superuser and inform eric that superuser is already editing the page
• when eric closes the page, eric gets the notification "eric is no longer editing this page" – correct would be to pass that information to superuser