mod_pagespeed forgets optimizations after a while

I've setup mod_pagespeed and it seems to work fine, but only when I reload a page. Minutes later the optimization is gone.

Here's a static site where full optimization is only done when you reload the page: twitterbogen.dk

On the first load the CSS files have no .pagespeed. in them. If you reload they do. Any idea why?

Here's my Apache Server Information.

And here's my mod_pagespeed configuration:

ModPagespeed on
AddOutputFilterByType MOD_PAGESPEED_OUTPUT_FILTER text/html
ModPagespeedFileCachePath            "/var/www/mod_pagespeed/cache/"
ModPagespeedGeneratedFilePrefix      "/var/www/mod_pagespeed/files/"
ModPagespeedEnableFilters rewrite_javascript,rewrite_css
ModPagespeedEnableFilters collapse_whitespace,elide_attributes
ModPagespeedEnableFilters extend_cache,combine_css,move_css_above_scripts,move_css_to_head,inline_css,inline_import_to_link,flatten_css_imports,inline_javascript,outline_javascript,rewrite_style_attributes,rewrite_images,sprite_images
ModPagespeedAvoidRenamingIntrospectiveJavascript on
ModPagespeedMessageBufferSize 100000