Crash-to-desktop using pistons.
A powered piston with "NaN" typed into its velocity field will crash the game to desktop in an instant.
-Place a piton with a battery attached.
-Open the piston's control panel.
-Ctrl+left click the piston's velocity slider.
-Type "NaN" into the field and hit 'ok'.
I recommend this gets fixed as this method can be used by a griefer as an easy way to repeatedly crash servers. This crashes the server as well as the client.