Index: wp-includes/comment.php
===================================================================
--- wp-includes/comment.php	(revision 23302)
+++ wp-includes/comment.php	(working copy)
@@ -1848,6 +1848,8 @@
 		endif;
 	endforeach;
 
+	$post_links = array_unique( $post_links );
+
 	do_action_ref_array( 'pre_ping', array( &$post_links, &$pung, $post_ID ) );
 
 	foreach ( (array) $post_links as $pagelinkedto ) {