in 16 9 project a choose "external preview" and image is letter boxed as it should be on 4 3 TV. then I disable a color correction effect on clip and image was not letterboxed on TV.

then i skip to a clip with noFX onit and they are not viewing as letterboxed on TV

only the cilp with FX on it view as letterboxed on TV even though this is true 16 9 footage from xl2 in 16 :9 project.