There is a bug where you can get to the multiplayer menu in the demo version of Minecraft.

NOTICE: You cannot join servers with this bug (if you attempt to, it will give the "Bad session token" error, as if you launched the game offline and then tried to join a server). You may be able to join LAN games though.

This bug affects all versions of Minecraft that have the demo feature and can open games to LAN. To re-produce:

1) Open demo Minecraft and click "Play Demo World".

2) Pause the game, open the world to LAN and turn on cheats.

3) Once the world is open to LAN, execute the command "/kick @p"

4) You will get kicked from the world. Click "Return to server list".

5) You will arrive in the server list. You're done!

How I suggest a fix: If the user is playing the demo version of Minecraft, have the game change "Return to Server List" to "Return to Title Screen" (and make it so the button actually returns you to the title screen.)