Oven heating element receives power when off?
Probably because it's a 240V oven, and the oven thermostatic switch only switches one side of the 240V.

American power is 240V, but wired with a center-tap on the transformer, with neutral attached at the center-tap and ground bonded there.   This gives 120V from either "hot" wire to the neutral, which is how most of your receptacles are wired.  Your oven uses both "hot" legs, with 240V between them.  It is also grounded to the center.  If the thermostat switch only switches one leg, that is adequate for controlling the oven, but it means the other leg is always connected to the heating element, so it is 120V above the grounded oven chassis.