I don't know anything about that model but it sounds like "drive by wire" power steering. If it is "drive by wire" power steering, all the steering wheel does is tell the power steering pump what you want it to do, and there is no direct linkage between the steering wheel and the actual steering hardware, so you can continue to keep turning the steering wheel forever, and all that it does is indicate your "wanting" to turn sharper, and the steering pump simply stops trying to turn the front wheels any further once they'e reached their stops.
Like I said, I don't know if that's what you've got, but it sounds like it.
Can you steer it without the engine running? If so, then my theory is shot.
Something is wrong. I'm trying to remember where the steering shaft terminates, my guess is at the pump. My steering wheel has about 2 turns lock-to-lock, and it will not go further. I would assume there is a lock at the pump that has failed.
By continuing to turn the wheel beyond the practical limits of travel, you are putting a strain on the hydro system. It's the equivalent of holding the deck actuator in the full up or down position.
This should be repaired. If you look at the steering shaft, look for something broken or cracked. My gut feeling is something near the pump.
Maybe it's just loose where the steering wheel attaches to the shaft right at the steering wheel hub. Maybe enough friction there to turn the shaft until it reaches it's limit, then you're just freewheeling the steering wheel on the shaft, albeit with some resistance.
Maybe there's a set screw somewhere to get the steering wheel to "bite" into the shaft and it's loose?
Looking on the Cub site parts viewer for the 3205 it looks like your steering shaft has a knurled or keyed end, so not likely that's freewheeling unless somehow you stripped it. It was tricky finding the right views.. if you go there, the steering wheel is in the "Dash" section and the shaft is in the "Pedestal" section.
I have a 3205 tore down right now and I recall the owner talking about a similar problem a while back(a year or two back). I'll ask him about it and check out the mechanism and get back to ya as soon as I have time.