If the OP isn't using digital thermometers with probes then chances are the hot side is too hot and the snake is trying to escape the heat by burrowing on the cool side and laying on top of the hide.

When I had a heat spike in my rack, all of my snakes sat on top of their hides. I wouldn't have even noticed the heat spike except for the fact that every single one was siting on top of the hides in the middle of the day.