PHP时区列表不一致

so I'm using drupal 6's date_timezone_names to generate a list of timezones:

/**
 * A translated array of timezone names.
 * Cache the untranslated array, make the translated array a static variable.
 *
 * @param $required
 *   If not required, returned array will include a blank value.
 * @return
 *   an array of timezone names
 */
function date_timezone_names($required = FALSE, $refresh = FALSE) {
  static $zonenames;
  if (empty($zonenames) || $refresh) {
    $cached = cache_get('date_timezone_identifiers_list');
    $zonenames = !empty($cached) ? $cached->data : array();
    if ($refresh || empty($cached) || empty($zonenames)) {
      $data = timezone_identifiers_list(DateTimeZone::ALL_WITH_BC);
      // Use include instead of include once in case the function gets
      // refreshed via devel or other API and is called more than once.
      if (module_exists('date_php4')) {
        include('./'. drupal_get_path('module', 'date_php4') .'/date_php4_missing_data.inc');
      }
      foreach ($data as $delta => $zone) {
        // Because many time zones exist in PHP only for backward
        // compatibility reasons and should not be used, the list is
        // filtered by a regular expression.
        if (preg_match('!^((Africa|America|Antarctica|Arctic|Asia|Atlantic|Australia|Europe|Indian|Pacific)/|UTC$)!', $zone)) {
          // https://github.com/Br3nda/drupal-module-date/blob/master/date_api.module
          $zonenames[$zone] = $zone;
        }
      }
      // If using PHP4, filter the list down to only the timezones
      // the PHP4 wrapper has data for.
      if (module_exists('date_php4')) {
        foreach ($missing_timezone_data as $zone) {
          unset($zonenames[$zone]);
        }
      }

      // If using Event, further filter the list down to only
      // zones that exist in the event module.
      if (module_exists('event') && db_table_exists('event_timezones')) {
        $result = db_query("SELECT name FROM {event_timezones} ORDER BY name");
        $names = array();
        while ($row = db_fetch_array($result)) {
          $names[] = str_replace(' ', '_', $row['name']);
        }
        foreach ($zonenames as $name => $zone) {
          if (!in_array($name, $names)) {
            unset($zonenames[$name]);
          }
        }
      }
      if (!empty($zonenames)) {
        cache_set('date_timezone_identifiers_list', $zonenames);
      }
    }
    foreach ($zonenames as $zone) {
      $zonenames[$zone] = t($zone);
    }
  }
  $none = array('' => '');
  return !$required ? $none + $zonenames : $zonenames;
}

notice that eventually it calls timezone_identifiers_list(DateTimeZone::ALL_WITH_BC)

but then this sometimes returns inconsistent list...sometimes timezones such as Asia/Chita (GMT+8) is present in the list...othertimes, that timezone doesn't exist in the list....also note that Asia/Chita is NOT in date_php4_missing_data.inc

any idea why this would happen? in what scenario would $data = timezone_identifiers_list(DateTimeZone::ALL_WITH_BC); return inconsistent list of timezones?

Another timezone that sometimes appear sometimes doesnt: Asia/Srednekolymsk ... notice that this also is NOT in date_php4_missing_data.inc

Both Asia/Chita and Asia/Srednekolymsk were added to the tzdb in 2014f (announcement here). This update corresponds to PHP's timezonedb version 2014.6.

You can see the current version of timezonedb installed by timezone_version_get(), as documented here.

It is entirely possible to have PHP installations with different versions of the timezonedb, whether due to running an older version of PHP itself, or having manually updated the timezonedb PECL package. If you care about up-to-date time zones, then you should subscribe to the IANA tz announcements mailing list, and apply corresponding updates to PHP's timezonedb as necessary.