Description:
------------
I use session_set_save_handler() to define my own session handler. It can read session values, but can't write them. But the function work well when I run my script on php 5.1.4. 

Session is stored in database in my script. When I store session in files, session is written well.

Reproduce code:
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The functions except for DBSessionWrite are omitted. PDO_MYSQL is used.

function DBSessionWrite($aKey,$aVal)
{
	global $_sessiondb,$_sessiontable;
	$sql = "SELECT lastupdated FROM ".$_sessiontable." WHERE sessionid=?";
	$stmt = $_sessiondb->prepare($sql);
	$stmt->execute($aKey);
	if($stmt->fetchColumn()) {
		$sql = "UPDATE ".$_sessiontable." SET datavalue=?, lastupdated=? WHERE sessionid=?";
		$stmt = $_sessiondb->prepare($sql);
		$stmt->execute(array($aVal,time(),$aKey));
	}
	else {
		$sql = "INSERT INTO ".$_sessiontable." VALUES (?,?,?)";
		$stmt = $_sessiondb->prepare($sql);
		$stmt->execute(array($aKey,time(),$aVal));
	}
	return $stmt->rowCount();
}


session_set_save_handler("DBSessionOpen", "DBSessionClose", "DBSessionRead", "DBSessionWrite", "DBSessionDestroy", "DBSessionGC");
session_start();

$session_idencode = md5($_SERVER["REMOTE_ADDR"]);
if($session_idencode != $_SESSION['idencode']) {
	session_regenerate_id(true);
	$_SESSION['idencode'] = $session_idencode;
}

Expected result:
----------------
One new row should appear in the session table.

Actual result:
--------------
No new row appear.