Incorrect user loaded by argument handler

I have a custom page which lives under user/%user/foobar path.

function MY_MODULE_menu() {
  $items = array();
  $items['user/%user/foobar'] = array(
    'title' => 'Foobar',
    'title callback' => 'MY_MODULE_foobar_title_callback',
    'title arguments' => array(1),
    'description' => 'Displays account balance of the current user.',
    'access callback' => 'MY_MODULE_foobar_access_callback',
    'access arguments' => array(1),
    'page callback' => 'MY_MODULE_foobar_page_callback',
    'page arguments' => array(1),
    'type' => MENU_LOCAL_TASK,
  );
  return $items;
}

(Title callback appends %user's name as a suffix to this page's title.)

When I check the foobar page with my administrator user (uid = 21) the result is correct, I see my user's name in the page title, but when I check an another user's (uid = 13671) page I still see my user's name in the page title, however it should be user 13671's username. If I put a dpm() to MY_MODULE_foobar_access_callback() callback to see what arguments this function gets in the $account parameter then the result speaks for itself.