I have a quite complex PHP class, reponsible for creating and printing meta_boxes, generating and saving meta fields, …

Each meta_box (object of class) has its own save function, that updates meta data of post (fields for them are instances of another class) as well as its post_excerpt and post_content. Yep, it’s probably a little complicated, but as I’m only starting with OOP, I’m pretty happy with it so far.

TL;DR, THE PROBLEM: With wp_update_post() called on save_post hook, I get an infinite loop. This issue is documented on WP codex as well as mentioned here on WPSE: How to avoid infinite loop in save_post callback.

If you are calling a function such as wp_update_post that includes the save_post hook,
your hooked function will create an infinite loop. To avoid this, unhook your function
before calling the function you need, then re-hook it afterward.

Source: Codex

This is a very simplified version of a code I am using:

class MetaBox {

    public function __construct() {
        // a lot of stuff, hooks and other function initiations
        add_action('save_post',array($this,'save_box'), 20);
    }

    // more stuff

    function save_box() {
        // verify nonces, bail out on autosave, ajax, cron, ...

        switch ($this->id) {
            case 'editor':
            case 'postexcerpt':

                // remove action
                remove_action('save_post', array($this,'save_box'));
                // bail out on post_revision
                if (!wp_is_post_revision($post_id) ){

                    $post = array(
                        // post id
                        'id'    => $post_id,
                        // tosave: either post_content or post_excerpt
                        // value: pulled from static associative multi-array inside MetaBox
                        $tosave => self::$meta[$this->id][$this->id]
                    );
                    wp_update_post($post);          
                }

                // add action back  
                add_action('save_post', array($this, 'save_box'));

            break;
            default:
                // some saving functionality for meta values, that WORKS just fine
            break;
        }
    }
}

I am getting an infinite loop with PHP error notice: Undefined index: ID in XXX/web/wp-includes/post.php on line 2987

Am I removing/adding save hook wrong? Does it have something in common with using the save function non-statically?

I am of course happy to provide the rest of the relevant code, if there’s no apparent problem with this structure.

EDIT

The infinite loop problem is gone – as @TheDeadMedic mentioned, problem lied at not matching priority.

To remove a hook, the $function_to_remove and $priority arguments must match when the
hook was added. This goes for both filters and actions. No warning will be given on
removal failure.

Codex: http://codex.wordpress.org/Function_Reference/remove_action

EDIT 2

As PHP is a case sensitive language, Undefined index ID notice problem lied in my $post array (parameter of wp_update_meta). The ID key must be specified uppercase.

$post = array(
    'ID' => $post_id    // ID must be uppercase
)

/////

As my question turned out to be very localized, feel free to delete it. And thanks again for helping me!

Thanks in advance!