That's with previous gen 4.
*edit* Let me write this coherently.
Everstones with Masuda Method would cancel out the NATURE transfer in Gen IV, it did not affect shiny rates.
I was using an Everstone when my Eevee came out as a Shiny with the correct Nature. Since I only filled half a PC box... either I got REALLY lucky, or it doesn't do it this Gen. I can say though that my Eevees are not always the correct Nature/Ability as the parent though. We're talking about probably a 9/10 accuracy on nature/ability here though. That's with me throwing a random number out there--I could do way better extensive testing to nail this down...if I desired to.
Edit: I don't know why but there has been a slow spread of misinformation on this. I'm guessing someone found an old thread from gen IV and started spreading the rumor around.
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