[Plugin: WP Super Cache] pages not cached

Hi, I’m using WordPress MU and I noticed that only a few pages are cached. Homepage isn’t cached and nor are posts. The setting to cache front/home page has been switched off, but it still isn’t cached. For example:
http://mydomain.com/ <– not cached
http://mydomain.com/secondblog/ <– not cached
http://mydomain.com/secondblog/2009/08/mypost.html <– not cached
http://mydomain.com/secondblog/mypage.html <– cached

Another thing is that for the blog that is not the root blog, ismyblogworking reports that gzip compression is off, but when I request a page with the direct URL then GZIP is on. For example:
http://mydomain.com/secondblog <– gzip reported as off
http://mydomain.com/secondblog/mypage.html <– gzip reported as on

Help is appreciated in tackling this problem.

Thanks,
Erwin

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