I remember long ago on a vehicle I had with regular hydraulic power steering, if I turned the wheel quickly right and left several times, it would lock up as you describe. I figured at the time it was the pump unable to keep up with the demand of the steering unit. Maybe your issue is something like this? I can't believe it is a "control arm" issue. A ball joint or control arm would stay locked up or would only release with a resounding "CLUNK". This whole steering thing has me worried. I turn my wife loose in this vehicle every day, and I don't want this happening to her.