Bug in the validator or obscure error in my CSS?

I am trying to validate a CSS document with the W3C validator, and it's giving some warnings related to color and background-color that should not appear since, well, I don't have those issues present in my document. Having it incorrectly report a warning wouldn't be so much of a surprise, but it reports different warnings every time the SAME document is validated!

http://jigsaw.w3.org/css-validator/validator?uri=http%3A%2F%2Fstatic.petroules.com%2Fcss%2Fphotocrayze%2F0-site.css&profile=css21&usermedium=all&warning=2&vextwarning=false&lang=en

Try clicking that link to validate the document, and refresh a few times - notice it'll report a different set of errors each开发者_StackOverflow社区 time.

I can't figure this out for the life of me - is this a known issue? I've only been able to reproduce it with this particular document.

If you copy the CSS and paste it into here it validates without any warnings. I'd just put it down to validator weirdness.