User blog comment:Omega natsu2/Episode 201: Delivery, Review./@comment-4449950-20140927033705/@comment-24039250-20140928193641

I'm assuming that the reason the spirits are like this is because of the dark magic from eclipse. I wouldn't be surprised if Zeref's Magic seeped into the spirits and changed them, similar to how F-Lucy and F-Rogue had some Zeref Magic residue on them, but the difference is that the spirits got more of it in them so its affecting them entirely. Just a theory.