Esc key always unpauses the game in Demo mode

The bug

When in a submenu of the pause menu, pressing Esc takes you out of the pause menu entirely (back to the game) instead of going "back one level" and taking you back to the pause menu.

This issue is only present when running the game in Demo mode, and the behaviour is inconsistent with when the game is launched normally.

To reproduce

1. Run the game in Demo mode. You can do this manually by specifying the correct arguments to the client.jar or you can select a Mojang account that has not brought the game in the Launcher.

2. Click "Play Demo World" to create a new world

3. Press Esc to pause the game

4. Click "Options" to enter the Options menu

5. Press Esc to exit the Options menu

Expected behaviour

The game would go back to the pause menu

Actual behaviour

The game unpauses entirely