in deiner functions.php hast du "thumbnail_small" zwei mal drinnen, der zweite eintrag ersetzt den ersten:
"thumbnail_small" => get_thumbnail_resizer($image_row['image_media_file'], $image_row['image_thumb_file'], $image_row['image_id'], $image_row['cat_id'], $image_row['image_name'], $mode, $show_link,0, 50,50), // The last two values are "width, height"
"thumbnail_small" => get_thumbnail_small_code($image_row['image_media_file'], $image_row['image_thumb_file'], $image_row['image_id'], $image_row['cat_id'], $image_row['image_name'], $mode, $show_link),
lösche diese zweite Zeile, oder nimm einen anderen namen.
mfg Andi