Description:
------------
---
From manual page: http://www.php.net/datetime.format
---
What is happening:

DateTime()->format() method strange behaviour after DateTime->setTimezone().
Ignores the public date property, Expected return value (format mask applied) should be based on the current public timezone and date properties.

Format method should apply the argument format mask to the date property based on current timezone property. Instead it appears that an unknown/undocumented modification to the date property is applied.

test script outputs;

$nowUtc

object(DateTime)[2607]
  public 'date' => string '2014-02-13 02:42:48' (length=19)
  public 'timezone_type' => int 3
  public 'timezone' => string 'UTC' (length=3)

$nowUtc->format('Y-m-d h:i:s')

string '2014-02-13 02:42:48' (length=19)

$nowUtc->setTimezone( new \DateTimeZone( 'Australia/Sydney' ) )

object(DateTime)[2608]
  public 'date' => string '2014-02-13 13:42:48' (length=19)
  public 'timezone_type' => int 3
  public 'timezone' => string 'Australia/Sydney' (length=16)

$nowUtc->format('Y-m-d h:i:s')

string '2014-02-13 01:42:48' (length=19) // expected 2014-02-13 13:42:48 based on Australia/Sydney


What is 2014-02-13 01:42:48 from anyway!

Test script:
---------------
<?php
            $nowUtc = new \DateTime( 'now',  new \DateTimeZone( 'UTC' ) );
            echo '$nowUtc'.PHP_EOL;
            var_dump($nowUtc);
            $nowUtc = new \DateTime( 'now',  new \DateTimeZone( 'UTC' ) );
            echo '$nowUtc->format(\'Y-m-d h:i:s\')'.PHP_EOL;
            var_dump($nowUtc->format('Y-m-d h:i:s'));
            $nowUtc->setTimezone( new \DateTimeZone( 'Australia/Sydney' ) );
            echo '$nowUtc->setTimezone( new \DateTimeZone( \'Australia/Sydney\' ) )'.PHP_EOL;
            var_dump($nowUtc);
            echo '$nowUtc->format(\'Y-m-d h:i:s\')'.PHP_EOL;
            var_dump($nowUtc->format('Y-m-d h:i:s'));exit;
?>

Expected result:
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format method should apply the argument format mask to the date property based on current timezone property.

Actual result:
--------------
Instead it appears that an unknown/undocumented modification to the date property is applied.