When you load a "debug mode" world, and you find a comparator in subtraction mode, right-click the comparator (to change its mode to comparison), the item in front of it (in the direction it points towards) is immediately updated. If it's standing on air (pressure plate, other comparator), the updates destroys it, makes it drop an item, and the map immediately creates it back. If the clicked comparator is pointing towards another comparator, the "update-destroy-drop-get back" thing is cycle hundreds of times per second, and the game quickly crashes.

Not sure why is that.