Variants are not updated with variant SKU

[tibomogul]

            if(product_load_object.variants.size == values.size)
              product_load_object.variants.each_with_index {|v, i| v.sku = values[i].to_s }
              product_load_object.save
            else
              puts "WARNING: SKU entries did not match number of Variants - None Set"
            end

Above code will not save the sku changes on the variants if the product object and variants have been saved already. Probably occurs in some other fields, as I see the same pattern.