[wp-trac] [WordPress Trac] #42572: Can't delete custom taxonomy tags from a post

[WordPress Trac]

#42572: Can't delete custom taxonomy tags from a post
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 Reporter:  thrica        |      Owner:
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Taxonomy      |    Version:  4.9
 Severity:  normal        |   Keywords:
  Focuses:                |
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 Symptoms are the same as #39388: I can add terms in my custom taxonomy to
 a post, but I can't remove them. I'm not using any of the filters
 mentioned in that ticket. Based on logging all SQL queries on saving a
 post, it looks like removing a category triggers a query like:

 {{{
 DELETE FROM wp_term_relationships WHERE object_id = 1470 AND
 term_taxonomy_id IN ('7')
 }}}

 No DELETE query at all is running when I try to remove the custom
 taxonomy, so it's not a malformed query. Same problem whether I'm using
 the classic editor, the quick editor, or Gutenberg.

 As a further wrinkle, in the classic editor, my terms don't even show up
 in the checkboxes in the sidebar (all of them are unchecked), though they
 do show up on the front end, in the quick editor, and in Gutenberg.

 This didn't always happen, but I don't recall the version it started with.
 Disabling all plugins doesn't fix it, neither does clearing out my
 functions.php entirely, and neither does changing 'hierarchical' to false.

 My arguments for registering the taxonomy are as follows:
 {{{
 $args = [
         'labels' => [ /* a bunch of strings */ ],
         'public' => true,
         'hierarchical' => true,
         'show_in_rest' => true,
         'rewrite' => ['hierarchical' => true],
         'query_var' => 'idea'
 ];
 }}}

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Ticket URL: <https://core.trac.wordpress.org/ticket/42572>
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