On many rapid-fire circuits, i have a repeater that gets locked to stop the pulse. If the repeater is off when it is locked, it works the way it is supposed to, but if it's on, it continues to carry the pulse at the same rapid-fire rate, making it hard to turn off because i have to keep doing it until it lands on the off state. Try making a rapid-firing circuit with a repeater, then try locking it.