I know that it's also related to PHP but sadly no one knew anything there so I try here... :)
At the PHP manual of PDOStatement::closeCursor it's written that "This method is useful for database drivers that do not support executing a PDOStatement object when a previously executed PDOStatement object still has unfetched rows. If your database driver suffers from this limitation, the problem may manifest itself in an out-of-sequence error.". Anyone know if the PostgreSQL driver suffer from this problem or not?