Ticket #17816: 17816.2.diff

wp-admin/includes/update-core.php

@@ -420 +420 @@
                                         if ( ! $wp_filesystem->copy($from . $distro . 'wp-content/' . $file, $dest . $filename, FS_CHMOD_FILE) )
                                                 $result = new WP_Error('copy_failed', __('Could not copy file.'), $dest . $filename);
                                 } else {
-                                        if ( $wp_filesystem->is_dir($dest . $filename) )
+                                        if ( $wp_filesystem->is_dir($dest . $filename) && 'twentyeleven' !== $filename )
                                                 continue;
 
                                         $wp_filesystem->mkdir($dest . $filename, FS_CHMOD_DIR);