This is as designed:
1. The Connection bar buttons are NOT linked directly to the Editor, so if you use these thinking that they switch the editor, they do not and have never done.
2. The 'switch sessions' button in the Editor toolbar is really designed for sharing the contents of the Editor, to run in a different database, so if this is your intention, then only use the 'switch session' button to toggle the Editor with another database.
3. If you only ever want to have one Editor window available, then you would always have to use the 'switch session' button on the toolbar, and not the button on the connection bar.
4. Toad was designed to have a separate editor for each connection. Our recommendations are to create new sessions using the Session | New Connection menu item, or the 'New Connection' button on the main toolbar
