=== modified file 'modules/book/book.module'
--- modules/book/book.module	2006-12-29 07:41:44 +0000
+++ modules/book/book.module	2007-01-05 15:13:18 +0000
@@ -781,7 +781,7 @@ function book_recurse($nid = 0, $depth =
  */
 function book_node_visitor_html_pre($node, $depth, $nid) {
   // Remove the delimiter (if any) that separates the teaser from the body.
-  $node->body = str_replace('<break>', '', $node->body);
+  $node->body = str_replace('<!--break-->', '', $node->body);
 
   // The 'view' hook can be implemented to overwrite the default function
   // to display nodes.

=== modified file 'modules/node/node.module'
--- modules/node/node.module	2007-01-04 09:53:58 +0000
+++ modules/node/node.module	2007-01-05 15:13:02 +0000
@@ -146,7 +146,7 @@ function node_teaser($body, $format = NU
   $size = variable_get('teaser_length', 600);
 
   // Find where the delimiter is in the body
-  $delimiter = strpos($body, '<break>');
+  $delimiter = strpos($body, '<!--break-->');
 
   // If the size is zero, and there is no delimiter, the entire body is the teaser.
   if ($size == 0 && $delimiter === FALSE) {
@@ -738,7 +738,7 @@ function node_prepare($node, $teaser = F
  */
 function node_build_content($node, $teaser = FALSE, $page = FALSE) {
   // Remove the delimiter (if any) that separates the teaser from the body.
-  $node->body = str_replace('<break>', '', $node->body);
+  $node->body = str_replace('<!--break-->', '', $node->body);
 
   // The 'view' hook can be implemented to overwrite the default function
   // to display nodes.
@@ -2199,7 +2199,7 @@ function node_preview($node) {
 function theme_node_preview($node) {
   $output = '<div class="preview">';
   if ($node->teaser && $node->teaser != $node->body) {
-    drupal_set_message(t('The trimmed version of your post shows what your post looks like when promoted to the main page or when exported for syndication. You can insert the delimiter "&lt;break&gt;" (without the quotes) to fine-tune where your post gets split.'));
+    drupal_set_message(t('The trimmed version of your post shows what your post looks like when promoted to the main page or when exported for syndication. You can insert the delimiter "&lt;!--break--&gt;" (without the quotes) to fine-tune where your post gets split.'));
     $output .= '<h3>'. t('Preview trimmed version') .'</h3>';
     $output .= node_view(drupal_clone($node), 1, FALSE, 0);
     $output .= '<h3>'. t('Preview full version') .'</h3>';

=== modified file 'modules/system/system.install'
--- modules/system/system.install	2007-01-03 11:10:58 +0000
+++ modules/system/system.install	2007-01-05 15:12:04 +0000
@@ -3452,12 +3452,11 @@ function system_update_1017() {
 }
 
 /**
- * Change break tag.
+ * Change break tag (was removed, see 1020).
  */
 function system_update_1018() {
-  $ret = array();
-  $ret[] = update_sql("UPDATE {node_revisions} SET body = REPLACE(body, '<!--break-->', '<break>')");
-  return $ret;
+  variable_set('update_1020_ok', TRUE);
+  return array();
 }
 
 /**
@@ -3479,6 +3478,19 @@ function system_update_1019() {
 }
 
 /**
+ * Change break tag back (was removed from head).
+ */
+function system_update_1020() {
+  $ret = array();
+  if (!variable_get('update_1020_ok', FALSE)) {
+    $ret[] = update_sql("UPDATE {node_revisions} SET body = REPLACE(body, '<break>', '<!--break-->')");
+  }
+  variable_del('update_1020_ok');
+  return $ret;    
+}
+
+
+/**
  * @} End of "defgroup updates-4.7-to-5.0"
  */