多个PHPSESSID cookie和浏览器不保留任何内容

Question

我从yii应用程序的登录请求中获得了2个PHPSESSID设置的Cookie标头。

Date: Thu, 05 Dec 2013 02:19:44 GMT 
Server: Apache/2.2.22 (Ubuntu) 
X-Powered-By: PHP/5.3.10-1ubuntu3
Set-Cookie: PHPSESSID=3lkhjlsv967n56horpcl3n7gl5; path=/
Expires: Thu, 19 Nov 1981 08:52:00 GMT 
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 
Pragma: no-cache 
Set-Cookie: PHPSESSID=sctb6cd1snbd5g2esv1mn2lug7; path=/ 
Content-Length: 3 
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: text/html; charset=utf-8

浏览器不会保留任何内容，也不会将其发送回来以备将来使用。知道这是怎么回事吗？