WP super cache no debug log / wrong timestamp

Hi !
I’ve been playing with wp-supercache for a long time now.
Unfortunately I’ve change my server and I have now some issue with the plugin.

Installation is fine, and configuration goes well. .htaccess files are modified and the wp-content/cache folder contains the test file.

But here comes the trouble :

Cache Tester

Test your cached website by clicking the test button below.

Fetching http://ela-dev.draft.lu/ to prime cache: OK

Fetching first copy of http://ela-dev.draft.lu/: OK (1.html)

Fetching second copy of http://ela-dev.draft.lu/: OK (2.html)

The pages do not match! Timestamps differ or were not found!

Looking at the header information for the two url we can see :

Accept-Ranges:bytes
Cache-Control:max-age=3, must-revalidate
Connection:Keep-Alive
Content-Encoding:gzip
Content-Length:11881
Content-Type:text/html
Date:Wed, 06 Mar 2013 22:11:37 GMT
ETag:"2161-e969-4d748da7bb480"
Expires:Wed, 06 Mar 2013 22:11:40 GMT
Keep-Alive:timeout=2, max=1000
Last-Modified:Wed, 06 Mar 2013 22:10:10 GMT
Server:Apache/2.2.16 (Debian)
Vary:Accept-Encoding,Cookie

and

Accept-Ranges:bytes
Cache-Control:max-age=3, must-revalidate
Connection:Keep-Alive
Content-Encoding:gzip
Content-Length:11904
Content-Type:text/html
Date:Wed, 06 Mar 2013 22:11:59 GMT
ETag:"2160-e961-4d748da10e4c0"
Expires:Wed, 06 Mar 2013 22:12:02 GMT
Keep-Alive:timeout=2, max=1000
Last-Modified:Wed, 06 Mar 2013 22:10:03 GMT
Server:Apache/2.2.16 (Debian)
Vary:Accept-Encoding,Cookie

The content length is different (I do not know why as there is no dynamics content on the page)

As I can not see any debug infos how could I debug ?

Thanks !

http://ww.wp.xz.cn/extend/plugins/wp-super-cache/