Accidentally leaving your PTO on and accidentally hitting the switch to raise the dump box, and not paying attention and not noticing your box is going up.
They are supposed to. But I've heard from drivers in the dump truck industry that the alarms are often disabled by drivers because "they are annoying".
My tractor I can't dump the airbags if I'm going over 10km/h, can't release the 5th wheel slider if trailer parking brakes are released, and tons of other safety features.