Hello Michael Beckwith,
Thank you for your prompt reply. Your below comments led me to do some further testing and I have found two items that seem to represent issues with backward compatibility.
Several months ago I created a custom post type with two custom taxonomies and then deactivated the plugin after pasting the code into the functions.php file.
Then today I wanted to add a new custom post type and taxonomy. So I updated and activated cptui plugin and added a taxonomy and post type pair. I erased the code for those original post types and taxonomies from the functions.php file, expecting to put them back with the new code in the export tab.
However, first the original taxonomies were unattached from their designated post type. So I re-attached them and saved. Then I had to edit the prior existing post type so it would be registered in the export file. (Simply opening in the editor and saving was sufficient) After that, I was able to paste the code for the taxonomies and post types back into my functions.php file and deactivate the plugin. The post types and taxonomies remain functional now.
Since the plugin worked perfectly, I did not suspect a problem with the export program. But now that I understand it, I will not have the problem again. However, it might be advisable to add some instructions for long time users who want to export code and have pre-existing post types and taxonomies made by cptui.
Regards,
Vincent Clark
PS: I am available to beta test anything you are working on at no charge, gratis.