[Plugin: WP Super Cache] Conflict with DirectoryIndex in Apache

I found super cache might be conflict with directory index settings when the gzip mode is on.
For example, I use DirectoryIndex command in httpd.conf to set cover.html as the default index page for wp.mydomain.com instead of index.php. If I start the wp super cache and turn on the gzip mode, everytime I visit wp.mydomain.com the default page will become the cached index.php, just bypassing the settings in httpd.conf.
That’s weird, I don’t know if it’s fixable.
Anyone can help me? Thanks.
I use the latest version of WP (2.6.5) and Wp super cache (0.8.6) now.