It’s due to Author
being an existing method name on the Versioned
class, so the code gets a bit confused when it tries to display it. Changing the variable name fixes this, as you’ve discovered.
There’s a bit of info on this old thread: lessons/v4/adding-custom-fields-to-a-page having issues with a varchar value not displaying.
(and yes, the lessons do need to be updated to reflect this)