The fourth edition of Catan and its related expansion was originally published with tiles of a particular thickness. When they decided to publish the Explorers & Pirates Expansion, they felt they needed thicker tiles due to the constant tile flipping. So they started printing the base game and all the expansions (with the exception of C&K) with thicker tiles to match in 2012. -- My source is a phone call with the publisher. I have two copies, one of each thickness.
This is the 2013 version. It has the thicker tiles.
It has an image of the base game box in the lower left corner.