Taxonomy terms loses hierarchy in admin backend list screen when 'Tags' is set in settings

Problem description

The hierarchy of the terms was showing on the front-end and in the 'Parent' field under 'Advanced Options' in the 'Edit Term' admin page. In the beginning everything worked fine in the admin backend. But the terms started showing alphabetically without grouping in the admin taxonomy screen. Also the arrows shown normally to order the terms were gone. As well as the ability to drag and drop.

Possible variables

Content was imported using the WordPress importer module.

Problem solution

In 'Edit Vocabulary' in 'Settings' check to see if 'Tags' is checkmarked. If it is, uncheck it, and save. Go back to the list menu. Everything came back on. 'Multiple select' does work as expected.

Follow up actions

Filing bug report with WordPress Importer module and Drupal to allow further examination of the issue.

Related forum topic: Cannot see and set a taxonomy's hierarchy!