When you say "pulled back over the saddle," how far back are you? You should ride a spinning bike the same as you would a real bike. Imagine you're on your own bike, climbing a heavy hill. The saddle would just be touching your inner thigh. If you were pulled waaaaay back over the saddle, I think something bad might happen--you could potentially pull the front of the bike up off of the ground, and, well, you get the picture. Try not to exaggerate your form on the spinning bike. And remember, if it doesn't feel right to you, don't do it. Keep it simple and just ride your bike.