I have the same problem.   I'm not sure what difference a seat switch would make   Mine just disconnects the autosteer, nothing else.   So if I'm in the seat or not, the tractor still goes, it just wanders off the line and gradually turns.   I really don't see the purpose of shutting off the autosteer but letting the tractor continue.   Every year I've usually got a spot where the corn is crooked because autosteer shut off and I didn't catch it right away.