This is with version 3.8 on Amazon S3. The stylesheet path is blank when I have CDN support turned on. This is probably because I changed from @import to <link rel="stylesheet" type="text/css" href="
vBulletin 3.8 typically uses the @import and we support that directly, since it allows vBO to determine if the stylesheet is external or internal. I would recommend reverting it back to how vBulletin typically handles it.
Wouldn't call it terrible really and afaik it has no impact on performance, <link> is mostly used in places where there are multiple CSS files which isn't the case with vB 3.8.