PDO prepared statements sometimes returns empty resultset

Hi, I'm trying to get some data form a MySQL db using PDO and prepared statement, but I noticed that sometimes it fetches an empty result set, but sometimes does what it's supposed to do - returns the whole result set. The environment is WinXP SP2 Home, Apache 2.2.4, PHP 5.2.1 and MySQL 5.0.27. Here is some code: $db = new PDO( 'mysql:host=localhost;dbname=name_of_db', 'user_name', 'password', array (

     PDO::ATTR_PERSISTENT => true

) ); $db->query('SET CHARACTER SET utf8'); $stmt = $db->prepare("CALL sp_get_all_currencies(:lang_id)"); $stmt->bindValue(':lang_id', $currenctLanguageId, PDO::PARAM_INT); $stmt->execute(); $currencies = $stmt->fetchAll(); So here, $currencies sometimes is an empty array, and after a refresh of the browser it populates. I also noticed that it works ok with $db->query(), but query doesn't have that fancy param binding (I think). Is there some caching or something... Is this a bug in PHP or I'm not getting the picture right? Regards, Emil Ivanov