Upravit functions.php v šabloně Twenty Eleven:
function wp36510_remove_singular_class( $classes ) {
$index = array_search( 'singular', $classes );
if ( false !== $index ) {
unset( $classes[ $index ] );
}
return $classes;
}
add_filter( 'body_class', 'wp36510_remove_singular_class' );
Zdroj: https://wordpress.org/support/topic/wp-45-and-twentyeleven-theme-problem#post-8277245