Hi,
There seems to be a problem indeed.
Could you replace the line:
$checkfields = array('product_name','product_description','prices','images','discount','product_url','product_weight','product_weight_unit','product_keywords','product_meta_description','product_dimension_unit','product_width','product_length','product_height','files');
by:
$checkfields = array('product_name','product_description','prices','images','discount','product_url','product_weight','product_weight_unit','product_keywords','product_meta_description','product_dimension_unit','product_width','product_length','product_height','files','product_contact');
in the file administrator/components/com_hikashop/classes/product.php and try again ?