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.

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