Wow. That's very interesting; I didn't know you could reverse it. Anyways, I checked and neither the rheostat or the heat pad plug in the other way.

But I think I figured it out. This is really weird. The little red light on my beardie's rheostat (which is the exact same) becomes bright when it is up all the way and goes off when I turn it all the way down. As a last resort, I tried turning the rheostat for my BP all the way "down" so the light went off. I can't be sure yet, but the thermometer above the heat pad went up 4 degrees. If it keeps going up, I guess the problem is solved... I feel pretty stupid that I didn't try that before.