Visting a topic in the styles demo returns 500 error

1. Visit the 3.2 styles demo (I couldn't find a 3.3 demo at all).
2. Visit any topic, like the 'normal topic'.
3. You should see a white page. In my console it states there was an 500 Internal Server Error when the page was requested.

I've tried on Safari & Chrome and both produce the same result.

Original report was made in the phpBB.com forums: community/viewtopic.php?f=64&t=2613871