Ticket #28541: 28541.diff

wp-includes/post-template.php

@@ -473 +473 @@
          * @param string $class   A comma-separated list of additional classes added to the post.
          * @param int    $post_id The post ID.
          */
-        return apply_filters( 'post_class', $classes, $class, $post->ID );
+        $classes = apply_filters( 'post_class', $classes, $class, $post->ID );
+
+        return array_unique( $classes );
 }
 
 /**
@@ -666 +668 @@
          * @param array  $classes An array of body classes.
          * @param string $class   A comma-separated list of additional classes added to the body.
          */
-        return apply_filters( 'body_class', $classes, $class );
+        $classes = apply_filters( 'body_class', $classes, $class );
+
+        return array_unique( $classes );
 }
 
 /**