zen_image() and online documentation

Having read this article on image handling in the ZC docs http://www.zen-cart.com/content.php?72-my-images-are-distorted-fuzzy-squished-help I had edited my widths in Images admin to zero

However on looking at /includes/functions/html_output.php in zen_image() I see

 // use old method on template images
    if (strstr($src, 'includes/templates') or strstr($src, 'includes/languages') or PROPORTIONAL_IMAGES_STATUS == '0') {
      return zen_image_OLD($src, $alt, $width, $height, $parameters);
    }

And then in function zen_image_OLD() I see

if ( (CONFIG_CALCULATE_IMAGE_SIZE == 'true') && (empty($width) || empty($height)) ) {

Now the database value 0 with not cause PHP's empty() to return true.

When I re-edited my widths in the admin and saved empty values the layout works as intended.

I'd love an explanation for why the docs are like that.

Thanks.

Have you some URLs to a few of the Products that do not have the images sizing correctly?

What settings are you using on Configuration ... Images ...