Index: src/wp-includes/post.php
===================================================================
--- src/wp-includes/post.php	(revision 31458)
+++ src/wp-includes/post.php	(working copy)
@@ -3965,6 +3965,10 @@
 	 *
 	 * The dynamic portions of the hook name, `$new_status` and `$post->post_type`,
 	 * refer to the new post status and post type, respectively.
+	 * 
+	 * publish_{$post->type} fires on first publish and subsequent updates.
+	 * If you are looking to only fire a callback when $post->post_type is first
+	 * published, use transition_post_status instead.
 	 *
 	 * @since 2.3.0
 	 *