Steps to reproduce

In session 1 (user A):

1. Create a new document in the Documents module, or open an existing one for editing.
2. Click the "Open in new tab" icon at the top right of the editor.
   
3. In the new tab, edit part of the document and save.

In session 2 (user B):
4. Open the same document from the Files module.

Bug
The two users don't see each other in the document or eachother's changes