User blog comment:Relikz/Chapter 364: Tartarus Arc, Part 1: Immorality and Sinners, Review./@comment-213.89.161.219-20131222095953/@comment-2214433-20131224231101

No, that's actually wrong, double issue in case of weekly manga magazines means that one issue covers two weeks. In other words, the magazine isn't released in one of those two weeks. And no, it doesn't (generally) contain more pages or anything. Mashima just tends to be an exception in such cases as he's capable of drawing at incredible pace.