Yes, PHP 5.6 defaults SoapClient() to require SSL verify_peer, and since the Interworx API SSL cert is not valid it's an issue. We are disabling verify_peer (reluctantly) in v4, and fixing another bug that prevents you from using http:// instead of https:// when adding an Interworx server to the module.
Edit: This may be helpful in explaining the issue http://stackoverflow.com/questions/18465567/php-soapclient-verify-peer-true-fails-with-ca-signed-certificate