Change the depth attribute of wp_dropdown_categories from -1 to 0 to fix

the hierarchical view

order-bender.php

@@ -89,7 +89,7 @@ function primary_taxonomy_term_meta_box($post, $callback_args)
 			'id' => $this->unique_prefix . '_' . $taxonomy->name . '_primary_term',
 			'class' => $this->unique_prefix . '_primary_term',
 			'echo' => 1,
-			'depth' => -1,
+			'depth' => 0,
 			'hierarchical' => 1,
 			'show_option_none' => __( '— Select —' ),
 			'option_none_value' => '0',