dependent fields appear only on blur in ie7 and ie8

ctools_include('dependent');

  $form['test'] = array(
    '#type' => 'fieldset',
    '#title' => t('Test'),
 '#collapsible' => FALSE,
  );

 $form['test']['foo'] = array(
   '#type' => 'checkbox',
   '#title' => t('Foo'),
   '#default_value' => FALSE,
 );
 $form['test']['bar'] = array(
   '#type' => 'fieldset',
   '#process' => array('ctools_dependent_process'),
   '#dependency' => array('edit-foo' => array(1)),
   '#input' => TRUE,
   '#id' => 'bar',
   '#prefix' => '<div id="bar-wrapper">',
   '#suffix' => '</div>',
 );
 $form['sale']['ec80']['ec80_serial'] = array(
   '#value' => t('Bar'),
 );
 return $form;

this works as desired in all current browsers:

1. Click on the 'foo'-checkbox
2. the 'foo'-checkbox get checked and
3. the 'bar'-fieldset appears

but in IE7 and 8:

1. Click on the 'foo'-checkbox
2. the 'foo'-checkbox get checked and
3. the 'bar'-fieldset doesn't appear

when I now click on something else (ergo: 'foo' looses its focus), the 'bar'-fieldset appears