User blog comment:FairyRaven/Fairy Tail Chapter 337: The Golden Plains, Review and Commentary/@comment-77.194.131.180-20130701090541

Mashima answered about this arc in volume 38 questions and answers, it seems that he changed the concept of his story for this arc, here the link : http://mangahelpers.com/forum/showthread.php/23840-Volume-Covers-Color-Pages-Misc./page33