Randomly (but seemingly more when restarting an application or under a higher load), certain CSS files will return a 500 error for no apparent reason.
bug.zip - a skeleton application which can trigger it
bug.png - a screenshot
However, this is highly intermittent, so it's actually quite hard to trigger. we see it more when restarting large applications, like the cfwheels core, and it's only either both normalize.min.css OR milligram.min.css OR both; (but never cfwheels.css) which makes me think that the regex is choking on the comments, or minified nature of those files in some sort of race condition? Or something.