Index: wp-includes/post-template.php
===================================================================
--- wp-includes/post-template.php	(revision 4891)
+++ wp-includes/post-template.php	(working copy)
@@ -80,7 +80,7 @@
 		$page = count($pages); // give them the highest numbered page that DOES exist
 
 	$content = $pages[$page-1];
-	if ( preg_match('/<!--more(.+?)?-->/', $content, $matches) ) {
+	if ( preg_match('/<!--more\s*(?:\/)?-->/', $content, $matches) ) {
 		$content = explode($matches[0], $content, 2);
 		if ( !empty($matches[1]) && !empty($more_link_text) )
 			$more_link_text = strip_tags(wp_kses_no_null(trim($matches[1])));
Index: wp-includes/post.php
===================================================================
--- wp-includes/post.php	(revision 4891)
+++ wp-includes/post.php	(working copy)
@@ -74,7 +74,7 @@
 // get extended entry info (<!--more-->)
 function get_extended($post) {
 	//Match the new style more links
-	if ( preg_match('/<!--more(.*?)-->/', $post, $matches) ) {
+	if ( preg_match('/<!--more\s*(?:\/)?-->/', $post, $matches) ) {
 		list($main, $extended) = explode($matches[0], $post, 2);
 	} else {
 		$main = $post;