Ticket #13246: 14433.diff

wp-includes/post.php

@@ -2096 +2096 @@
                         $post_category = array();
         }
 
+        // Make sure the category is set in [0] if there is only one
+        if ( 1 == count($post_category) && empty( $post_category[0] ) )
+                $post_category[0] = array_shift($post_category);
+
         if ( empty($post_author) )
                 $post_author = $user_ID;