Index: modules/book/book.admin.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/book/book.admin.inc,v
retrieving revision 1.38
diff -u -p -r1.38 book.admin.inc
--- modules/book/book.admin.inc	20 Oct 2010 01:31:06 -0000	1.38
+++ modules/book/book.admin.inc	8 Nov 2010 16:56:14 -0000
@@ -175,6 +175,10 @@ function _book_admin_table($node, &$form
  * @see book_admin_edit()
  */
 function _book_admin_table_tree($tree, &$form) {
+  // The delta must be big enough to give each node a distinct value.
+  $count = count($tree);
+  $delta = ($count < 30) ? 15 : intval($count / 2) + 1;
+
   foreach ($tree as $data) {
     $form['book-admin-' . $data['link']['nid']] = array(
       '#item' => $data['link'],
@@ -190,7 +194,7 @@ function _book_admin_table_tree($tree, &
       'weight' => array(
         '#type' => 'weight',
         '#default_value' => $data['link']['weight'],
-        '#delta' => 15,
+        '#delta' => $delta,
         '#title' => t('Weight for @title', array('@title' => $data['link']['title'])),
         '#title_display' => 'invisible',
       ),
Index: modules/book/book.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/book/book.module,v
retrieving revision 1.555
diff -u -p -r1.555 book.module
--- modules/book/book.module	5 Nov 2010 19:47:20 -0000	1.555
+++ modules/book/book.module	8 Nov 2010 16:56:14 -0000
@@ -506,11 +506,12 @@ function _book_add_form_elements(&$form,
 
   $form['book']['plid'] = _book_parent_select($node->book);
 
+  // @see _book_admin_table_tree(). The weight may be larger than 15.
   $form['book']['weight'] = array(
     '#type' => 'weight',
     '#title' => t('Weight'),
     '#default_value' => $node->book['weight'],
-    '#delta' => 15,
+    '#delta' => max(15, abs($node->book['weight'])),
     '#weight' => 5,
     '#description' => t('Pages at a given level are ordered first by weight and then by title.'),
   );