Meta value does not save for scheduled posts

I had a similar problem with a custom metabox. The problem was the use of $post_id inside the save-function. Using global $post and then $post->ID solved the problem for me.

function save_metabox(){
    global $post;

    if(defined('DOING_AUTOSAVE') && DOING_AUTOSAVE){
        return $post->ID;
    }

    $myData = $_POST['my data'];
    update_post_meta($post->ID;, $myData);
}