Hi Alistair!
Perhaps you are confusing the custom fields functionality provided by WordPress with the Additional Fields feature built in to our plugin (that can be configured from Events > Settings > Additional Fields and then set in events meta box)?
If you want to use WordPress’s custom fields (I’m guessing that is what you are trying to do, based on the screenshot – let me know if I’m off-beam here though) then you should use the functions made available by WordPress to display them rather than our template tags.
Does that help?