Change wordpress shortcode pattern to allow single and enclosed version of a tag in one post/page.

wp-plugins-mod.php

<?php
// For WP 4.0
// In file wp-includes/shortcodes.php line 228 and following,
// replace the whole return (or comment out the original code) with this line:
//
// (I know it's ugly, but it works. 
//  Basically we just replaced this part:
//  --> '\\[(?!\\/\\2\\])' // An opening bracket not followed by the closing shortcode tag
// with:
// --> '\\[(?:(?!\\/\\2\\]|\\2))'
//         ^^              ^^
//         Add grouping    ^^
//                         Not an opening tag with the same name (\\2 is the backreference to the matched tag.)
// )
//

return '\\[(\\[?)('.$tagregexp.')(?![\\w-])([^\\]\\/]*(?:\\/(?!\\])[^\\]\\/]*)*?)(?:(\\/)\\]|\\](?:([^\\[]*+(?:\\[(?:(?!\\/\\2\\]|\\2))[^\\[]*+)*+)\\[\\/\\2\\])?)(\\]?)';