problem with call to hook_user in custom module

Hi

The API for hook_user says that elements can be inserted into $user and should be done so on 'load'. The following simple module demonstrates that information inserted into $user on 'load' doesn't survive by printing the information that should have been inserted into $user in a block. The 'specialstring' which is inserted into $user cannot be printed when the block is rendered.

<?php
function block_example_help($section) {
  switch ($section) {
    case 'admin/modules#description':
      // This description is shown in the listing at admin/modules.
      return t('An example module showing how to define a block.');
  }
}

function block_example_block($op = 'list', $delta = 0, $edit = array()) {
  switch ($op) {
    case 'list':
      $blocks[0]['info'] = t('Example: configurable text string');
      return $blocks;
    case 'configure':
      $form = array();
      if ($delta == 0) {
        $form['block_example_string'] = array(
          '#type' => 'textfield',
          '#title' => t('Block contents'),
          '#size' => 60,
          '#description' => t('This string will appear in the example block.'),
          '#default_value' =>
            variable_get('block_example_string',  t('Some example content.')),
        );
      }
      return $form;
    case 'save':
      if ($delta == 0) {
        variable_set('block_example_string', $edit['block_example_string']);
      }
      return;
    case 'view': default:
      switch ($delta) {
        case 0:
          $block['subject'] = t('Title of block #1');
          $block['content'] = block_example_contents(1);
          break;
      }
      return $block;
  }
}
function block_example_contents($which_block) {
global $user;
  if ($which_block == 1) {
    $output = variable_get('block_example_string',  t('A default value.'));
    $output .="<br />user name is : $user->name";
    $output .="<br />user special string is : $user->specialstring";
    return $output;
  }
}

function block_example_user($op, &$edit, &$user, $category = NULL) {
  switch ($op) {
    case 'load':
        $user->{specialstring} = "Hello World";
    break;
  }
}
?>

I also tried all of the following in vain:

        $user->specialstring = "Hello World";
        $user->{'specialstring'} = "Hello World";
        $user['specialstring'] = "Hello World";

I also loaded a clean system for drupal-cvs as of 10:30am PDT (GMT-8:00) on Jan 26 and the problem persists.

Mark