Comparators don't recalculate output signals when side input signal is a 1 tick pulse

While trying to create a comparator not gate, it came to my attention that when a 1 tick pulse is pushed through a repeater into a redstone dust, and then is fed into the side input of a comparator in subtraction mode, the output is not updated. However, when you replace the repeater in the above example with redstone, the comparator is updated, even though pistons now have instant logic.