WebKit does not render pages correctly when the CSS page does not have a Content-Type: text/css header. While I realise this is also a bug at the server side, that the server should return a Content-Type: text/css header, given that the referring page has a link rel="stylesheet" type="text/css", I believe WebKit could be more forgiving.
Not sure what the version is, but I have confirmed this bug today by downloading latest Google Chrome browser.
I believe that our behavior matches the relevant specifications. If your page is in quirks mode, we'll happily load a stylesheet regardless of MIME type. If your page is in strict mode, we require that stylesheets be served with the appropriate MIME type.