Hook priority order not respected when callbacks added in-hook

[Rarst]

Sequence of actions producing unexpected result:

1. Some callbacks are added to hook
2. One of callbacks runs at priority 0 and adds more callbacks to same hook
3. Remaining callbacks do not fire in expected (priority ascending) order

Code demonstrating the issue:

class Nervous_Breakdown {

	public $priorities = array();

	public function __construct() {

		add_action( __CLASS__, array( $this, 'add' ), 0 );
		add_action( __CLASS__, array( $this, 'log' ), 0 );
		add_action( __CLASS__, array( $this, 'log' ), 10 );

		do_action( __CLASS__ );
		var_dump( 'Priorities fired in order: ' . implode( ' >> ', $this->priorities ) );
		// Result is 'Priorities fired in order: 0 >> 10 >> 2'
	}

	public function add(  ) {

		add_action( __CLASS__, array( $this, 'log' ), 2 );
	}

	public function log() {

		global $wp_filter;
		$this->priorities[] = key( $wp_filter[current_filter()] );
	}
}

new Nervous_Breakdown();

[SergeyBiryukov]

Related: #9968, #17817, #19015, #20998, #21169, #23035, #26239.

[DrewAPicture]

Just tested, and can confirm that #17817 would fix this.

[Rarst]

Confirm as fixed.