The closest I know of is Blurry bred back to son and the results were no blurry babies, now that doesn't mean that it won't turn blurry over time. The hets never turned blurry either so it's doubtful it's a codom. I have seen blurry balls come in since the early 90's and that's a long time for them to be around and so far no definitive genetics have happened to my knowledge.