Fortunately I have two dev sites going for this project (where I'm using Posts 2 Posts). In my particular case I've used a modified p2p-outline-classes_posts_to_posts.php file and that is where I've noticed the issue. The connected class no longer displays, rather it displays itself.
I've rolled back WP to 3.4.2 and it's working again. Scribu if you're interested in taking a look at this issue I can provide more detail.