Description:
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On the Debian Wheezy distribution, since the last update of PHP5 to the version 5.4.35-0+deb7u2, the serialization of DateTime seems to be broken.
The problem occurs periodically and is reproducible with difficulties.

In my test environment, the problem occurs when I want to read data that are stored into the Redis Server.
Examples:

During the authentication, when the problem occurs, the stack trace is :
[{"message":"Error: Invalid serialization data for DateTime object in \/var\/www\/XXXX\/front\/vendor\/symfony\/symfony\/src\/Symfony\/Component\/Security\/Core\/Authentication\/Token\/AbstractToken.php line 163","class":"Symfony\\Component\\Debug\\Exception\\FatalErrorException","trace":[{"namespace":"","short_class":"","class":"","type":"","function":"","file":"\/var\/www\/XXXX\/front\/vendor\/symfony\/symfony\/src\/Symfony\/Component\/Security\/Core\/Authentication\/Token\/AbstractToken.php","line":163,"args":[]}]}]

Another example during data retrieval from cache:
{"message":"Error: Invalid serialization data for DateTime object in \/var\/www\/XXXX\/front\/src\/XXXX\/APIBundle\/Service\/YYYYService.php line 144","class":"Symfony\\Component\\Debug\\Exception\\FatalErrorException","trace":[{"namespace":"","short_class":"","class":"","type":"","function":"","file":"\/var\/www\/XXXX\/front\/src\/XXXX\/APIBundle\/Service\/YYYYService.php","line":144,"args":[]}]}]

I've found a recent bug report in the EZPublish project that seems to be built on Symfony 2 components: https://jira.ez.no/browse/EZP-23713. Attached files to this issue are interesting because we have a valid and an invalid DateTime serialization.

Then I've downgraded my Debian Wheezy PHP5 package to this version : 5.4.4-14+deb7u14 , and the problem doesn't exists.