CIOS60BF uses the app.1 from CIOS36 rev7 which doesn't have any problems with Mario Kart but probably has problems with the newer games. Your IOS249 is probably CIOS36 rev8 (or 9). rev8 was having problems with Mario Kart and some other games and thats why the CIOSCORP package of MiiWii is not fully rev8 dipped. Some IOSes uses the rev7 version for Mario Kart and other games to work. If you have CIOS36 rev8 installed you could try rev9, maybe it fixed the problem for Mario Kart?