It's a TWL_FIRM thing, actually. It also happens for users without CFW.On the unofficial bootstrap 6c6e60c, Mario Kart has duplicated pixels along the bottom of both screens. About 16? pixels above the bottom it just repeats once what was above it.
Just restarted the game and now it's gone: I didn't change any setting or change what I did in game.
Settings were Donor Rom ON(MKDS), Original sound quality, TWL speed/133, unofficial bootstrap.
EDIT: This is a bootstrap thing not a TWLoader thing, isn't it.