One problem related to brake light on has been reported for the 2010 Mazda CX9. The most recently reported issues are listed below.
Vehicle brakes lighting dim while coming to a stop and can not be seen from other vehicles approaching from behind on the road. When not replaced, stop light will run continually or not function, potentially causing premature bulb failure, safety issues and/or the transmission will not shift out of park. A failed stoplight switch will prevent the brake light from illuminating when the brake pedal is applied that may cause a collision and a life lost.