User blog comment:IamJakuhoRaikoben/Chapter 357: The Nine Demon Gates, Review./@comment-1784397-20131026000339/@comment-7418318-20131026075956

Maybe they have some loose connection with Zeref and rather than Zeref consciously ordering them to attack, they were affected by the change in Zeref and thus got it into their minds to kill and rampage across the land.

I think that's even fit in nicely with Zeref not having his own feelings and powers under control.