Maybe Kubota does it different, but on my Branson and on other tractors too, once you get to full lock, the steering wheel stops turning. If the tractor is not running, the steering wheel will still have resistance and will turn the wheels, although it does take some serious force, which is normal. It also won't change position when driving on straight line.
So no, not all Orbitrol steering systems will free wheel and honestly, I don't really consider it normal to freewheel. But I'll dig into some Kubota service manuals to see what they do differently.