When creating a piklist field for a custom taxonomy on a cpt,
I can set 'scope' => 'post_meta' and provide a field name, and it will save the
id of the taxonomy term chosen to that custom meta field with the provided name.
This of course is not the same as using the built-in WP terms table, which allows the taxonomy to be edited in the admin page for the cpt normally.

To correct this, I change the scope of the piklist field to "taxonomy". Now it saves to the WP terms table, and the built-in WP mechanisms also work. However, what happens to 'field'? If I remove it, it no longer works, but what is it doing with it?

When the field is set as required and nothing is chosen, it doubles up the error message saying:

* <Label> is a required field
* <field name value> is a required field

This is ugly and broken.