Enabling realtime collaboration through the link from the warning message doesn't work when editing in-place

Steps to reproduce

1. Enable Realtime WYSIWYG from Administration
2. Login with an user (e.g. U1)
3. Edit a page in-place
4. Using another (incognito) window/tab, login with another user (e.g. U2)
5. Edit the same page by forcing the lock
6. With an user who is editing in-place (e.g. U1), untick 'Allow Realtime Collaboration' from the Save bar
7. Click 'Leave the collaborative session' button
8. On the yellow warning message that is displayed on the top of the page, click 'enabling realtime collaboration link'

Expected results

The user is connected to the realtime session again.

Actual results

Nothing happens, the link doesn't seem to be working.