A new feature was added in 3.7.17 to add the categories names to the body on single post pages. It does this by testing to see if the page is an archive pages (any multi post page). If so, it does not add the category names to the <body> statement.
Turns out that if you show your posts on the landing page, it is not considered an archive page like all other multi post pages (sigh)
To fix this issue you can edit function.php and change line 925 (version 3.7.18) from
HTML Code:
if (!is_archive()) {
to
HTML Code:
if (is_single()) {
or replace functions.php with the attached version. This will be fixed in the next release.
