This problem has been bothering me for a while now, and I only just came across the solution this week. The issue was that when you schedule a post for the future, when it does finally post it was seemingly not running the publish_post hook that I had set. Multiple solutions suggested using future_to_publish as a hook, and that did not work either. The actual solution was to hook to publish_future_post, but in addition the function I was executing had to be modified a bit.
The original function was something along these lines: When a post is published for the first time, post a link to it on Twitter. publish_post also fires when you update a post, so to make sure it was only posted on the original posting the accepted solution was to make sure post_date and post_modified dates were equal. Here is an simple example.
PHP Code:<?php
// accepted solution, but this will not work as expected
// on scheduled posts.
add_action('publish_post','bob_on_publish_post');
add_action('publish_future_post','bob_on_publish_post');
function bob_on_publish_post($id) {
$post = get_post($id);
if($post->post_modified != $post->post_date) return;
// la de da, doing stuff.
return;
}
?>
The reason this fails is that it turns out when a post is scheduled for future posting, post_date and post_modified are not equal after all. This issue caught me by surprise because it does not exist when working with Drafts. If the post is marked as draft, saved, and then manually published later, this test will still allow the hook to run. This is probably due to how WordPress handles filling up your database with redundant revisions, but it even works if you have a Plugin disabling revisions (like me).