[Plugin: WP Super Cache] Pages are regenerated each time

PHP Speedy and WP Super Cache are installed and setup ok.
However, the pages are regenerated each times : I got these in the end of the html :
<!– Dynamic page generated in 0.821 seconds. –>
<!– Cached page generated by WP-Super-Cache on 2009-06-16 10:28:29 –>

then :
<!– Dynamic page generated in 0.966 seconds. –>
<!– Cached page generated by WP-Super-Cache on 2009-06-16 10:31:49 –>

then :
<!– Dynamic page generated in 1.014 seconds. –>
<!– Cached page generated by WP-Super-Cache on 2009-06-16 10:32:08 –>

the refresh is done via https://web-sniffer.net/?url=https://www.malaiac.net/&submit=Submit&http=1.1&gzip=yes&type=GET&uak=0 (web sniffer), so no logged in users issues should arise (I doubt web sniffer ever made a comment on my blog)

Same thing if I crawl my blog with wget :
(example from a tag page ??
<!– Dynamic page generated in 1.998 seconds. –>
<!– Cached page generated by WP-Super-Cache on 2009-06-16 10:35:00 –>

<!– Dynamic page generated in 0.989 seconds. –>
<!– Cached page generated by WP-Super-Cache on 2009-06-16 10:35:32 –>

WP-Cache (67.45KB)
2 Cached Pages
0 Expired Pages

WP-Super-Cache (505.10KB)
12 Cached Pages
0 Expired Pages

What do you think ?