When editing a term with multiple parents and one of those parents is the root, then the <root> option is not preselected in the parent terms select box. This can result in unexpected data loss if saving such a term without reselecting the root parent.
The reason is that taxonomy_term_load_parents() does not return parent=0 since this is not a "real term" that exists in the taxonomy_term_data table.
Note, that lib/Drupal/taxonomy/TermFormController.php has a special case for preselecting parent=0 if the term has no parents.