Agreed this is not the best behavior. We found it simpler to adjust the code in include/func/func.product.php after:
Code:
$product['meta_description'] = trim($product['meta_description']);
$product['meta_keywords'] = trim($product['meta_keywords']);
add
Code:
if (empty($product['meta_description']))
$product['meta_description'] = trim(strip_tags(func_query_first_cell("SELECT descr FROM $sql_tbl[products_lng_current] WHERE productid='$productid'")));