wp_update_post() resetting term order

reset-term-order-bug.php

<?php

// Sample code to demonstrate a possible bug in core where
// wp_update_post() is resetting the term_order.
global $wp_taxonomies;

// Let core set the term_order field automatically.
$wp_taxonomies['category']->sort = true;

$post_id = wp_insert_post(
	[
		'post_title'   => 'Test Title',
		'post_content' => 'Test Content',
		'post_status'  => 'publish',
	]
);

$term_names = [
	'E) First Term',
	'Z) Second Term',
	'A) Third Term ',
];

$term_ids = [];

foreach ( $term_names as $term_name ) {
	$existing_term = term_exists( $term_name, 'category' );
	if ( is_array( $existing_term ) ) {
		$term_ids[] = $existing_term['term_id'];
	} else {
		$new_term = wp_insert_term( $term_name, 'category' );
		if ( is_array( $existing_term ) ) {
			$term_ids = $new_term['term_id'];
		}
	}
}

wp_set_post_terms( $post_id, $term_ids, 'category', false );

// Verify the terms are in sorted by the term_order.
$terms = wp_get_post_terms( $post_id, 'category', [ 'orderby' => 'term_order' ] );

foreach ( $terms as $term ) {
	var_dump( $term->name );
}

$post = get_post( $post_id );


var_dump( 'Calling wp_update_post()' );

// Update the post and then get the terms again.
wp_update_post(
	[
		'ID'         => $post_id,
		'post_title' => 'New Test Title',
	]
);

// Now the terms come back alphabetical, but they should still be by term order.
$terms = wp_get_post_terms( $post_id, 'category', [ 'orderby' => 'term_order' ] );

foreach ( $terms as $term ) {
	var_dump( $term->name );
}

sample-output.txt

/var/www/html/wp-content/plugins/sample-code/includes/test:79:
string(13) "E) First Term"
/var/www/html/wp-content/plugins/sample-code/includes/test:79:
string(14) "Z) Second Term"
/var/www/html/wp-content/plugins/sample-code/includes/test:79:
string(13) "A) Third Term"
/var/www/html/wp-content/plugins/sample-code/includes/test:82:
string(24) "Calling wp_update_post()"
/var/www/html/wp-content/plugins/sample-code/includes/test:96:
string(13) "A) Third Term"
/var/www/html/wp-content/plugins/sample-code/includes/test:96:
string(13) "E) First Term"
/var/www/html/wp-content/plugins/sample-code/includes/test:96:
string(14) "Z) Second Term"