Description:
------------
PHP-Version:
PHP 5.3.99-dev (cli) (built: Nov  1 2010 17:42:09) 
Copyright (c) 1997-2010 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2010 Zend Technologies

If a timezone is passed in the time-string to the constructor of the DateTime-Object, a subsequent add() call could result in incorrect results (if the add() call oversteps a daylight-saving time).

Test script:
---------------
// Gives expected result
$date = new DateTime('2010-10-31 01:00 CEST', new DateTimeZone("Europe/Zurich"));
$date->setTimezone(new DateTimeZone('Europe/Zurich'));
$date->add(new DateInterval('PT3H'));
echo $date->format('Y-m-d H:i:sP')."\n";

// Doesn't give expected result
$date = new DateTime('2010-10-31 01:00 CEST', new DateTimeZone("Europe/Zurich"));
$date->add(new DateInterval('PT3H'));
$date->setTimezone(new DateTimeZone('Europe/Zurich'));
echo $date->format('Y-m-d H:i:sP')."\n";

Expected result:
----------------
2010-10-31 04:00:00+01:00
2010-10-31 04:00:00+01:00


Actual result:
--------------
2010-10-31 04:00:00+01:00
2010-10-31 03:00:00+01:00