Yep, I know exactly what you mean. The related term field stores it’s data in postmeta and doesn’t use the taxonomy data tables in WordPress. It’s more of an alternative way to relate to taxonomy terms.
If you need to relate using taxonomies, you are better off just creating the taxonomy, linking it to the post type, and just use the standard user interface.
MasterPress 1.1.5 is now available. This release contains 2 very important compatibility fixes; PHP7 and WordPress 5. We have also: Fixed hardcoded http link to Google Maps JS (replaced with https)Added new “Google Maps API Key” field to Settings > MasterPressFixed Visual/HTML Editor tab JS bug Please install this update as soon as you can…
MasterPress requires a minimum of WordPress version 4.9, MySQL 5.6, and PHP version 5.6.20.
We also recommend that PHP is configured to use a memory limit of 64MB per request (128MB may be required for sites with higher complexity).
This plug-in is not compatible with the WordPress.com hosted service.