That is intended behaviour. 'Duplicate' is a bit of a misnomer as it only duplicates the settings and not the content. As a Pro subscriber, you can properly duplicate a page by using the transmogrifier to move the page to another game. Change the name of the page in your main game and then transmogrify it back again. Not ideal or intuitive but possible ;) There is a suggestion in the appropriate forum to enhance this aspect of the VTT if you want to lend weight to it though...
