logged in cookies expire 1 year ago

I’m building a jmeter project to test my wordpress website. The problem is that jmeter can’t login. I’ve discovered that the cookies that indicate that I’m logged in expire one year ago. Here’s a full response header from a request:

[BEGIN HEADERS]
Date: Thu, 02 Jun 2011 00:52:50 GMT
Server: Apache/2.2.17 (Unix) mod_ssl/2.2.17 OpenSSL/0.9.8r DAV/2 mod_fcgid/2.3.5 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635
Expires: Wed, 11 Jan 1984 05:00:00 GMT
Cache-Control: no-cache, must-revalidate, max-age=0
Pragma: no-cache
X-Frame-Options: SAMEORIGIN
Set-Cookie: wlmdebug=deleted; expires=Wed, 02-Jun-2010 00:52:50 GMT
wordpress_test_cookie=WP+Cookie+check; path=/
wordpress_301d4af26a250dc39b47a471b93029a0=+; expires=Wed, 02-Jun-2010 00:52:51 GMT; path=/wp-admin
wordpress_sec_301d4af26a250dc39b47a471b93029a0=+; expires=Wed, 02-Jun-2010 00:52:51 GMT; path=/wp-admin
wordpress_301d4af26a250dc39b47a471b93029a0=+; expires=Wed, 02-Jun-2010 00:52:51 GMT; path=/wp-content/plugins
wordpress_sec_301d4af26a250dc39b47a471b93029a0=+; expires=Wed, 02-Jun-2010 00:52:51 GMT; path=/wp-content/plugins
wordpress_logged_in_301d4af26a250dc39b47a471b93029a0=+; expires=Wed, 02-Jun-2010 00:52:51 GMT; path=/
wordpress_logged_in_301d4af26a250dc39b47a471b93029a0=+; expires=Wed, 02-Jun-2010 00:52:51 GMT; path=/
wordpress_301d4af26a250dc39b47a471b93029a0=+; expires=Wed, 02-Jun-2010 00:52:51 GMT; path=/
wordpress_301d4af26a250dc39b47a471b93029a0=+; expires=Wed, 02-Jun-2010 00:52:51 GMT; path=/
wordpress_sec_301d4af26a250dc39b47a471b93029a0=+; expires=Wed, 02-Jun-2010 00:52:51 GMT; path=/
wordpress_sec_301d4af26a250dc39b47a471b93029a0=+; expires=Wed, 02-Jun-2010 00:52:51 GMT; path=/
wordpressuser_301d4af26a250dc39b47a471b93029a0=+; expires=Wed, 02-Jun-2010 00:52:51 GMT; path=/
wordpresspass_301d4af26a250dc39b47a471b93029a0=+; expires=Wed, 02-Jun-2010 00:52:51 GMT; path=/
wordpressuser_301d4af26a250dc39b47a471b93029a0=+; expires=Wed, 02-Jun-2010 00:52:51 GMT; path=/
wordpresspass_301d4af26a250dc39b47a471b93029a0=+; expires=Wed, 02-Jun-2010 00:52:51 GMT; path=/
Last-Modified: Thu, 02 Jun 2011 00:52:51 GMT
Keep-Alive: timeout=5, max=95
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: text/html; charset=UTF-8

200 OK
[END HEADERS]

Notice that the expires value for each cookie is one year before the Date of the request. Why is that? Is this expected behavior?