That’s strange, on my testsite it’s working:
link_printscreen
and I only have this in child-theme functions.php:
function featured_image_caption () {
global $post;
$thumbnail_id = get_post_thumbnail_id($post->ID);
$thumbnail_image = get_posts(array('p' => $thumbnail_id, 'post_type' => 'attachment'));
if ($thumbnail_image && isset($thumbnail_image[0])) {
echo '<span class="thumb_excerpt">'.$thumbnail_image[0]->post_excerpt.'</span>';
}
}
add_action('graphene_after_post_content', 'featured_image_caption')