Hey Jeremy,
Thanks for writing in! As you can see from our shortcode demonstration page, this feature works as expected on our demo installations. It is likely that a third party plugin or script you have installed is creating a JavaScript error on your page, keeping this from working. Without a URL to your site, there is no way to tell for certain, but we recommend that you try disabling all third party plugins and scripts one by one to see which one could be causing the conflict.
Thanks!