XMLHttpRequest error with Github Pages and subdomain [duplicate]

This question already has an answer here:

• XMLHttpRequest cannot load is not allowed by Access-Control-Allow-Origin 4 answers

My custom domain is using my Github Pages source (domain.github.io), except a php file located at a subdomain on my account: http://ift.tt/1P3G0Vr to keep the info separate/private from Github. Now that my domain is going through Github Pages, I'm getting this error after my form submit.

The bizarre thing is, the form still works. It sends the text message, but I'm still getting the XMLHttpRequest error (and does not show ajax was successful).

Why is this an error if both domains are using domain.com?

XMLHttpRequest cannot load http://ift.tt/1P3G0Vr. Origin http://DOMAIN.com is not allowed by Access-Control-Allow-Origin. sendjquery-2.1.4.min.js:4:14958 ajaxjquery-2.1.4.min.js:4:10717 (anonymous function) formLogic.js:65 dispatchjquery-2.1.4.min.js:3:6472 handlejquery-2.1.4.min.js:3:3247

via Chebli Mohamed