After the release of 7.x-5.1, the -dev version used a class naming convention that ended up not matching the Drupal 8 class naming convention that was developed later.
Since many, many developers used the -dev version on production sites, the 7.x-5.2 release of Zen uses the same class naming convention that existed in the -dev version. This makes updating from the -dev version to 7.x-5.2 easy.
The 7.x-5.3 version of Zen, however, uses the class naming convention that matches the one developed for Drupal 8.
Please read the instructions at https://drupal.org/node/1588228 for information on how to upgrade your Zen sub-theme to this version or to 7.x-5.3.
- Update Normalize.css to 2.1.2.
- Add zen_no_wrapper layout for Mini Panels.
- Move all stylesheets from .info file into @import of styles.css