It seems that there's an automatic handbrake, or brake for all wheels when there is no driver inside of a vehicle. I understand that it's possibly there to prevent from vehicles to slide down slopes when there's no driver inside.
But this "feature" also prevents us from using propper towing, by using RopeX or towing railers.
So, if possible, please remove this to enable us modders using trailers or allowing us to tow vehicles.