Hmm, well I thought that the details[] array would be converted to be in the same POST string as the products data - not sure why that's not the case here. At least, that's how it works for the USPS module.

The only thing I can really think of that might cause it to work on one host and not the other would be your PHP version. Do you know what version you are using? If it's less than 4.4 I would see about upgrading. If you can update to PHP 5.2.5 you will be in even better shape. (PHP5 at least).