Index: wp-includes/query.php
===================================================================
--- wp-includes/query.php	(revision 23682)
+++ wp-includes/query.php	(working copy)
@@ -3647,13 +3647,16 @@
 	if ( is_single() || is_page() || is_feed() )
 		$more = 1;
 	$content = $post->post_content;
-	if ( strpos( $content, '<!--nextpage-->' ) ) {
+	if ( false !== strpos( $content, '<!--nextpage-->' ) ) {
 		if ( $page > 1 )
 			$more = 1;
 		$multipage = 1;
 		$content = str_replace("\n<!--nextpage-->\n", '<!--nextpage-->', $content);
 		$content = str_replace("\n<!--nextpage-->", '<!--nextpage-->', $content);
 		$content = str_replace("<!--nextpage-->\n", '<!--nextpage-->', $content);
+		// Ignore the nextpage tag at the beginning of content
+		if ( 0 === strpos( $content, '<!--nextpage-->' ) )
+			$content = substr( $content, 15 );
 		$pages = explode('<!--nextpage-->', $content);
 		$numpages = count($pages);
 	} else {