Content Length 0 When Posting

What would cause a POST to a third party to have a content length of 0? All the form data from the debug dump is there, and all the field mappings seem to be there. But when doing the actual post, the content length is 0 and no data is passed over.

Running 1.6.4, WP 4.1.2, Contact Form 7 4.1.1.

Thanks.

https://ww.wp.xz.cn/plugins/forms-3rdparty-integration/