IDENTITY() in subquery throws error

public function testIdentityFunctionInSubqueryClause()
{
    $sql = $this->_em->createQuery(
        "SELECT a
         FROM Doctrine\Tests\Models\CMS\CmsAddress a
         WHERE a.user IN (
             SELECT IDENTITY(a2.user)
             FROM Doctrine\Tests\Models\CMS\CmsArticle a2
         )"
    )->getSql();
}

1) Doctrine\Tests\ORM\Query\SelectSqlGenerationTest::testIdentityFunctionInSubqueryClause
Doctrine\ORM\Query\QueryException: [Syntax Error] line 0, col 85: Error: Expected Doctrine\ORM\Query\Lexer::T_FROM, got '('

/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/QueryException.php:42
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:380
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:255
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:1189
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:1280
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:2737
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:2228
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:2145
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:2121
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:2089
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:2064
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:1212
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:760
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:727
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:213
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query/Parser.php:288
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query.php:231
/Users/adrienbrault/Developer/php/mygithub/doctrine2/lib/Doctrine/ORM/Query.php:177
/Users/adrienbrault/Developer/php/mygithub/doctrine2/tests/Doctrine/Tests/ORM/Query/SelectSqlGenerationTest.php:1375