Make sure you re-enable Autolock after using the lock slider. Breifly shining a flashlight at the sensor or opening and closing the keyboard (after enabling Autolock) should fix it if it gets confused in the dark. The only way I know of to confuse it is to disable it in the light and enable in the dark (or vice versa). Please let me know if you find another repeatable way to confuse the latest version.

Thanks.