[wp-trac] [WordPress Trac] #48068: Weird behavior when setting hierarchical to false on the built-in taxonomy category

[WordPress Trac]

#48068: Weird behavior when setting hierarchical to false on the built-in taxonomy
category
--------------------------+-----------------------------
 Reporter:  kwellmann     |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Taxonomy      |    Version:  5.2.3
 Severity:  normal        |   Keywords:
  Focuses:                |
--------------------------+-----------------------------
 When altering the taxonomy args of the built-in taxonomy category and
 setting hierarchical to false unexpected things started to happen - tested
 on a fresh install of WordPress.

 {{{#!php
 <?php
 add_filter('register_taxonomy_args', function($args, $taxonomy) {
     if ($taxonomy == 'category') {
         $args['hierarchical'] = false;
     }

     return $args;
 }, 10, 2);
 }}}

 After adding the code above as a simple plugin and activating it:
 When moving the default post 'Hello world!' into trash the category
 changes from 'Uncategorized' to '1'.
 Restoring it changes the category again. This time to '2'. Looking at the
 edit-tags.php?taxonomy=category page there are now two additional terms
 ('1'  and '2') which have been automatically created.

 When creating a new post it gets the newly created term '1' assigned
 instead of 'Uncategorized'.

 When creating a new term with the name 'Test' and assigning it to my newly
 created post another term is automatically created ('5') which seems to
 replace term '2' since it is gone.

 The 'new' term names seem to be generated based on the ID from a previous
 term.

 On a side note:
 On the edit-tags.php?taxonomy=category page everything is now labeled with
 'Tag' instead of 'Category'.

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Ticket URL: <https://core.trac.wordpress.org/ticket/48068>
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