Enabling default taxonomy/term view, vocabulary fields disappear

Which version of Views do you use? CVS HEAD? Which version of D7 core do you use?

Can replicate with RC1 views 7.x-3.x-dev

I experience exactly the same issue when I activate the default view taxonomy_term. It's highly reproductible.
Drupal 7 RC-1
Views 7.x-3.x-dev

Can you describe step by step how to reproduce the problem?

Did you changed your taxonom/term view?

The view has row style node, so the terms are listed as links. So what's the reason the additional field to the term should be displayed.

Some screenshots might help. I can't reproduce it.

aaaaaaaaaaaaaaah.

But this will be a bit disapointing.

Views is a tool to build lists of items, here nodes.
So there will be no automatically build lists of items AND load the term and show the term.
But since views 3.x, it's possible to write a area handler which prints the stuff you want.
Maybe it would be even possible to be included in views: A area handler which renders a single entity in the header, based on manual settings or based on argument. You could create a new issue for this.

You can use hook_view_pre_render() in your template.php file to alter many parts of the view including title, header or footer as shown below.

Example:

function hook_views_pre_render(&$view) {
  // Optionally check display
  if($view->current_display == 'page') {
    // Use machine name for view.  In this case it is company_view
    // which is an example view for a Company that has the additional
    // text field of City and a taxonomy reference for State/Province.
    if($view->name == 'company_view') {
      // Get the taxonomy term id
      $tid = $view->args[0];
      // Verify its valid and load the taxonomy object
      if($tid && $term = taxonomy_term_load($tid)) {
        // Get the vocabulary id
        $vid = $term->vid;
        // Get the taxonomy id of the state/province.
        // We will get the term name later.
        $stateprov_tid = $term->field_state_province['und']['0']['tid'];
        // Get the city name, which is an extra field we added
        $city = $term->field_city['und']['0']['value']
        // Verify vid is valid and load vocabulary object
        if ($vid && $vocab = taxonomy_vocabulary_load($vid) ) {
          // Modify term name to include the vocabulary
          // name and update view title
          $term->name = $vocab->name . ": " . $term->name;
          $view->set_title($term->name);
        }
        // Optionally alter view header to include other fields,
        // in this example a city and state/province.
        if ($term->vocabulary_machine_name == 'company') {
          // Verify we have a valid state/province term
          // and load the object.
          if ($stateprov_tid && $stateprov_term = taxonomy_term_load($stateprov_tid)) {
            // Set the header value to City, State/Province.
            $header = $city . ", " . $stateprov_term->name;
            // Set the options for the view header
            $options = array(
              'id' => 'area',
              'table' => 'views',
              'field' => 'area',
              'empty' => FALSE,
              'content' => $header,
              'format' => 2,
              'tokenize' => 0,
              );
            // Update the view with the new header
            $view->set_item('default', 'header', 'area', $options); 
          }
        }
      }
    }
  }
}