Baumatic Oven Thermostat Problem?

Hi
My Baumatic oven is not working properly. THe thermostat light comes on when everything is turned off, and then goes out when you turn on the oven (i.e. the opposite of what it should do). The oven just seems to get hotter and hotter as if the thermostat isn't working. Is this a faulty thermostat? Could this be casued by the thermostat just coming out of place? I changed the element when that blew about 6 months ago and all has been fine since until now. Thanks for any help.