fla91 on "wp-super-cache - Same page cached in WP Cache & in WP Super cache"

Hi,

I had a look at my cached pages and saw that :

In WP-Cache
2 blog.prestamariage.fr/ blog.prestamariage.fr80/gzipfla91|1346571925|f1876312666b83aff814cc380feda619, 56

In WP-Super Cache
1 blog.prestamariage.fr/ 1181

The same page was already in cache of wp super cache, but when i went to the main url (blog.prestamariage.fr), it regenerated the page, and apparently cached it in wp cache.
Footer of page =

<!-- Dynamic page generated in 1.935 seconds. -->
<!-- Cached page generated by WP-Super-Cache on 2012-08-31 09:44:42 -->

<!-- Compression = gzip -->

Therefore, generated at time i accessed the page.

Is there a reason for that ?

Thanks in advance.
Fabien.

http://wordpress.org/extend/plugins/wp-super-cache/