Steps:
1. Add the Disconnect button to the toolbar of a session and save layout.
2. Close the session.
3. Open the session again and connect.
Result: The Disconnect button remains disabled (as if it hadn't connected yet). However, if you open one of the menus (even the Help menu), the button will become active again.
Added to bug list. There are probably other buttons that this kind of problem will happen with. A lot of the enable/disable testing of various menu commands is done when you popup the menu, which isn't going to work with the button on the toolbar.