Buggy behavior:
Run a single-player world from the single-player menu.
Type /stop as a command to exit the single-player game.
Exit to server selection menu, where you have to exit out of that and go back to the single-player menu.

Expected behavior:
Run a single-player world from the single-player menu.
Type /stop as a command to exit the single-player game.
Return to single-player menu ready to try another single-player world or restart the same game.