Looks like you beat me to it. I had the same problem with a site I run at work. Yes, it’s MIME misconfiguration – the CSS file isn’t being sent as type ‘text/css’, which Moz requires.
If you haven’t found another fix, create an .htaccess file on your pomona webspace with the line:
AddType text/css .css
or, if it’s just the one page, you could use an embedded style-sheet inside the page itself rather than an external one.