Why won't Drupal AHAH forms work within a block?

Question

I'm trying to get an AJAX-submitted (AHAH) form working to display in a block on the sidebar. For testing purposes, I'm using an example module called "Poof" from the Pro Drupal Development book: http://books.google.com/books?id=VmZrdGuBZCMC&lpg=PA269&ots=cnHiYG6kXn&dq=pro%20drupal%20development%20poof&pg=PA269#v=onepage&q=pro%20drupal%20development%20poof&f=false

The only thing I've added to the example so far is an implementation of hook_block, which looks like this:

  function poof_block($op = 'list', $delta = 0, $edit = array()) {
  switch ($op) {
    case 'list':
      $blocks[0]['info'] = t('poof');
      return $blocks;
    case 'view':
       $block['content'] =  drupal_get_form('poof_form');
       return $block;
  }
}

The AJAX module works fine when displaying on its own page (mydrupalsite.com/poof) but when I call the form with module_invoke('poof', 'block' ...) in a template file, the form submits as normal (sans AJAX) and refreshes the page.

I can't find a definitive answer for why this happens, though a found something tangentially related that suggests that maybe AHAH doesn't work within blocks. If that's so, why? Or better yet, what's a work-around. Do I have to put the on its own blank page and bring it in with an iframe? That sounds unnecessarily messy.

UPDATED: Here's more code for reference (again, it's from the Pro Drupal book)

function poof_form() {
  $form['target'] = array(
    '#type' => 'markup',
    '#prefix' => '<div id="target">',
    '#value' => t('Click the button below.'),
    '#suffix' => '</div>',
  );
  $form['submit'] = array(
    '#type' => 'button',
    '#value' => t('Click Me'),
    '#submit'=>false,

    '#ahah' => array(
      'event' => 'click',
      'path' => 'poof/message_js',
      'wrapper' => 'target',
      'effect' => 'fade',
    ),
  );

  return $form;
}

function poof_message_js() {
  $output = t('POOF!');
  drupal_json(array('status' => TRUE, 'data' => $output));
}