Ticket #23823: 23823.1.diff

wp-content/themes/twentythirteen/functions.php

@@ -447 +447 @@
 function twentythirteen_featured_gallery() {
         $pattern = get_shortcode_regex();
 
-        if ( preg_match( "/$pattern/s", get_the_content(), $match ) ) {
-                if ( 'gallery' == $match[2] ) {
-                        if ( ! strpos( $match[3], 'size' ) )
-                                $match[3] .= ' size="medium"';
-
-                        echo do_shortcode_tag( $match );
-                }
+        if ( preg_match( "/$pattern/s", get_the_content(), $match ) && 'gallery' == $match[2] ) {
+                add_filter( 'shortcode_atts_gallery', function( $atts ) {
+                        $atts['size'] = 'large';
+                        return $atts;                   
+                } );
+                echo do_shortcode_tag( $match );
         }
 }
 endif;