I downloaded and checked out the catablog plugin locally. The Plugin does seem to be kept up to date by the author, but the issue is that the items in the Catablog library aren’t actually Custom Post Types… They are a custom database creation by the author so they don’t follow the normal WP structure and filters that are used to enable and function my post duplication.
So, I guess you are correct that the issue most likely came about because it is an old plugin. It was most likely created before WP implemented the custom post type functionality as it exists today. The only thing I could suggest would be to ask the author of that plugin if they have any plans to convert the Catablog posts into actual Custom Post Types. Though, since they haven’t yet already I’m guessing they don’t have any plans… Custom Post Types where introduced a while back.