Do you have an example URL that does embed properly, preferably a working version of that same page, for comparison? It looks like Wordpress is trying to use OpenGraph, but the OG spec says:
The four required properties for every page are:
og:title[…]og:type[…]og:image[…]og:url
The only one that page is displaying for me is og:image, which is why we’re not oneboxing that URL properly. If Wordpress is presenting all the OG meta tags on one version of the page, but not on another, that would be… weird, but something you’d have to take up with Wordpress.