Missing #region_callback

When on a power menu manage fields page, e.g. admin/config/search/power_menu/fields/my_menu/fields, I get a fatal error:

Fatal error: Function name must be a string in /path/to/drupal/modules/field_ui/field_ui.admin.inc on line 156

This appears to b due to a missing $row['#region_callback'] value in field_ui.