WordPress: Enable [shortcode] shortcode (real thing) in core WP image captions

gistfile1.php

<?php
/**
 * Filter Caption shortcode attributes to enable the [shortcode] shortcode inside caption text
 * 
 * WP doesn't run do_shortcode on the 'caption' text value parsed out of [caption], which means
 * the [shortcode] shortcode doesn't work. 
 * 
 * We want [shortcode] to work but not necessarily any other shortcodes, so we will run do_shortcode()
 * only if [shortcode] is present. Running do_shortcode() this way will process all shortcodes
 * so beware any captions that for some reason also have a bad shortcode that will break formatting.
 * 
 * @param array $out atts array as determined by WP to be returned after filtering
 * @param array $pairs 
 * @param array $atts
 * @return filtered $out atts
 */
function gv_filter_shortcode_atts_caption_shortcode_shortcode($out, $pairs, $atts) {
	/**
	 * If the shortcode shortcode is present then process all shortcodes
	 * Note: This will process ALL shortcodes which could give insane results
	 */
	if (has_shortcode($out['caption'], 'shortcode')) :
		$out['caption'] = do_shortcode($out['caption']);
	endif;
	return $out;
}
add_filter('shortcode_atts_caption', 'gv_filter_shortcode_atts_caption_shortcode_shortcode', 10, 3);
?>