session_starts sends duplicate Set-Cookie

Description

The following code:

<?php

session_id('mysessionid');

session_start();
session_write_close();
session_start();

Resulted in this output:

HTTP/1.1 200 OK
Date: Mon, 19 May 2025 15:51:57 GMT
Server: Apache/2.4.62 (Win64) PHP/8.4.0 mod_fcgid/2.3.10-dev
X-Powered-By: PHP/8.4.0
Set-Cookie: PHPSESSID=mysessionid; path=/
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate
Pragma: no-cache
Set-Cookie: PHPSESSID=mysessionid; path=/
Content-Length: 0
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: text/html; charset=UTF-8

But I expected this output instead:

HTTP/1.1 200 OK
Date: Mon, 19 May 2025 15:51:57 GMT
Server: Apache/2.4.62 (Win64) PHP/8.4.0 mod_fcgid/2.3.10-dev
X-Powered-By: PHP/8.4.0

Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate
Pragma: no-cache
Set-Cookie: PHPSESSID=mysessionid; path=/
Content-Length: 0
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: text/html; charset=UTF-8

I tried with output buffering on and off. If I remove session_id() I cannot reproduce it again, but I only used it to create a reproducible example, as in the real project, it's sending duplicate headers even without it.

PHP Version

PHP 8.4 and Apache 2.4.62

> Apache/2.4.62 (Win64) PHP/8.4.0 mod_fcgid/2.3.10-dev

Operating System

Windows 10

ソースファイルもテストも指定されていません。まず、Apache 上の PHP 8.4 で、提示された session_id/session_start/session_write_close のシーケンスを再現し、その後、重複した Set-Cookie ヘッダーの原因となっているセッションの開始および終了の動作を追跡してください。重複が排除され、そのシーケンスを対象とするリグレッションテストが追加されれば完了です。