If the roll pin is broken, then I could certainly see it unwinding. Jack wouldn't lift the camper either? With properly functioning jacks, this won't be a concern, they will stay where you put them.
I raise them until only about an inch of the inner leg is exposed. This is just before any bottoming of the screw or clicking of the safety clutch. I can see no reason to wind them right to the top. There have been some opinions in the past about an internal O-ring that might keep water out if you wind them right up, but if you have had one apart you know that is incorrect.
