Older versions of prettify have an issue with missing newlines in IE10, so all code blocks render on 1 line. This pull request will upgrade Prettify to the latest version (r224) and resolves the newline issue.
More details @ http://yuilibrary.com/projects/yui3/ticket/2532534
Upgraded prettify to r224
Looks like you accidentally blew away Selleck's custom Handlebars language handler.
Unrelated to this pull request: do you think you guys could fork Selleck and maintain it under the yui org? I have no reason to actively maintain it now, and I'd hate to block you guys if I can't get around to accepting PRs quickly.
Reintroduced YUI customizations to Prettify
Issuing PR against yui#5 instead