diff -u b/src/Entity/TaxonomyMenu.php b/src/Entity/TaxonomyMenu.php
--- b/src/Entity/TaxonomyMenu.php
+++ b/src/Entity/TaxonomyMenu.php
@@ -221,7 +221,7 @@
 
     // Please note: if menu_parent_id is NULL, it will not update the hierarchy properly.
     if (empty($menu_parent_id)) {
-      $menu_parent_id = str_replace('main:', '', $this->getMenuParent());
+      $menu_parent_id = str_replace($this->getMenu() . ':', '', $this->getMenuParent());
     }
 
     // TODO: Consider implementing a forced weight based on taxonomy tree.
diff -u b/src/Form/TaxonomyMenuForm.php b/src/Form/TaxonomyMenuForm.php
--- b/src/Form/TaxonomyMenuForm.php
+++ b/src/Form/TaxonomyMenuForm.php
@@ -84,10 +84,7 @@
     asort($custom_menus);
 
     $menu_parent_selector = \Drupal::service('menu.parent_form_selector');
-    $menu_names = $custom_menus;
     $available_menus = $custom_menus;
-    // limit to main menu
-    // $available_menus = ['main' => $available_menus['main']];
     $menu_options = $menu_parent_selector->getParentSelectOptions(null, $available_menus);
 
     $form['menu_parent'] = [