I have the same problem on my test site. I use the Theme "Hybrid Structure" (child theme of Hybrid).
It does work perfectly when I add the code in "post.php" in the parent theme directory (without the global declaration). However, it doesn't work when I add it in "function.php" of the child theme, even if I add the global declaration at the top of "function.php".
I'm not really good in php programming, maybe I missed something concerning global variable declaration?
Thank you so much for your great plugin! Even in beta version, it answered many of my needs and simplified a lot my work.