It took us (IT engineers) 30 seconds to understand that one page can have many pads (sessions?) opened at once.
Our mistake was to share the address from the browser address bar (index.php?title=User:Bedhed&action=edit) instead of the pad address provided within the editor (index.php?title=User%3ABedhed&action=edit&collaborate=true&padId=81).
This feature is great and very powerful, but perhaps too much.
Also, even if I see the benefits of sessions, I wonder if the related use cases are so important, in comparison to the possible UX issues, and also merging issues.
On top of my head : multiple sessions should be an advanced option. Users editing one page share only one default pad. By expanding the sessions menu, a user can then click a link that explicitly says "Open a new session". Once he did, he then have the relative pad url available.
And to conclude, a choice should be made between "PAD" and "SESSION", using two words to say one thing is confusing.