User blog comment:FairyRaven/Fairy Tail Chapter 346: Retrogression Magic, Review and Commentary/@comment-15382134-20130802190848/@comment-4829046-20130803084325

The reason is on the main page.

"There will be no new Fairy Tail chapter either next week or the week after as Chapter 346 is released as a double issue."

And this has happened many times in FT manga so I find it a bit strange this question is up again.