Description:
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A DateTime object that is created using a timestamp (with the "@$iTimestamp" notation) but without a explicitly given time zone (in the constructor) invalidly reports its time zone as the default time zone, although its time zone really is UTC. Converting it to the default time zone corrects this behaviour.

I know that this bug is somewhat similiar to http://bugs.php.net/bug.php?id=41912, that was marked as "bogus", but I think the demonstration code makes it clearer that in this case it is really buggy behaviour.

In fact, the UNIX timestamp is quite clearly defined as "the number of seconds since 1970-01-01 00:00:00 UTC" and thus it should be time zone independant.

Reproduce code:
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$oDateTest = new DateTime("@0", new DateTimeZone(date_default_timezone_get()));
echo "timestamp 0, constructed with default time zone (".$oDateTest->getTimezone()->getName()."): " . $oDateTest->format("Y-m-d H:i:s")."<br />";
$oDateTest->setTimezone(new DateTimeZone("UTC"));
echo "timestamp 0, constructed with default time zone, set to ".$oDateTest->getTimezone()->getName()." afterwards: " . $oDateTest->format("Y-m-d H:i:s")."<br />";
$oDateTest->setTimezone(new DateTimeZone(date_default_timezone_get()));
echo "timestamp 0, constructed with default time zone, then set to UTC and then to default time zone (".$oDateTest->getTimezone()->getName().") again: " . $oDateTest->format("Y-m-d H:i:s")."<br />";

$oDateTest = new DateTime("@0");
echo "timestamp 0, constructed with default time zone (".$oDateTest->getTimezone()->getName()."): " . $oDateTest->format("Y-m-d H:i:s")."<br />";
$oDateTest->setTimezone( new DateTimeZone(date_default_timezone_get()));
echo "timestamp 0, constructed with default time zone, explicitly set to default time zone (".$oDateTest->getTimezone()->getName().") afterwards: " . $oDateTest->format("Y-m-d H:i:s")."<br />";


Expected result:
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timestamp 0, constructed with default time zone (Europe/Berlin): 1970-01-01 01:00:00
timestamp 0, constructed with default time zone, set to UTC afterwards: 1970-01-01 00:00:00
timestamp 0, constructed with default time zone, then set to UTC and then to default time zone (Europe/Berlin) again: 1970-01-01 01:00:00
timestamp 0, constructed with default time zone (Europe/Berlin): 1970-01-01 01:00:00
timestamp 0, constructed with default time zone, explicitly set to default time zone (Europe/Berlin) afterwards: 1970-01-01 01:00:00

Actual result:
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timestamp 0, constructed with default time zone (Europe/Berlin): 1970-01-01 00:00:00 (Either the time zone or the reported time is WRONG)
timestamp 0, constructed with default time zone, set to UTC afterwards: 1970-01-01 00:00:00
timestamp 0, constructed with default time zone, then set to UTC and then to default time zone (Europe/Berlin) again: 1970-01-01 01:00:00
timestamp 0, constructed with default time zone (Europe/Berlin): 1970-01-01 00:00:00 (Either the time zone or the reported time is WRONG)
timestamp 0, constructed with default time zone, explicitly set to default time zone (Europe/Berlin) afterwards: 1970-01-01 01:00:00