If this is the ReadyStop system from NSA, the only way I can see it locking up the brakes without being pulled on from the front breakaway loop would be if the ReadyBrute/ReadyBrake applied the brakes and somehow the ReadyStop cable became jammed where it passes through the firewall. The ReadyStop cable is not in a casing like the ReadyBrake cable and there should be at least 3"-4" of slack in it between the brake peddle and the locking device. The slack should be wire tied where it can't be snagged by any moving parts of the vehicle.
