HTML5 CORS request fails in safari after redirect

I am crafting a CORS request with jQuery to accomplish a SSO type system. User logs into wordpress and with a hook at the same time also logs into Moodle. The problem I'm having is that in Safari (and only safari ~7+) when the inital POST request is set to moodlesite.com/login/index.php there is a redirect to: moodlesite.com/login/index.php?testsession=user_id. When this redirect occurs Safari drops the applicable CORS headers and then the request to the redirected URL fails.