Voila:
Dans includes/functions.php
ligne 212
remplacer
$description = (!empty($image_row['image_description'])) ? format_text($image_row['image_description'], 0) : REPLACE_EMPTY;
par
$description = (!empty($image_row['image_description'])) ? format_text($image_row['image_description'], 1) : REPLACE_EMPTY;
et les balises html seront "parsées"