I checked your setup and I see you're using an old version of X and Cornerstone. Please update X and Cornerstone to the latest versions to avoid such conflicts and potential errors. You can find the latest version numbers here: (http://theme.co/changelog/) Then you can compare them to what's installed on your site.
If you find anything to be out of date, you can review our update guide.
This should fix the issue. Let us know how this goes!