[bug] warning on valid selector

Hey guys,
I was reading the CSS 2.1 Specification, & I found this example:
Here, the selector matches all SPAN elements whose "hello" attribute has
exactly the value "Cleveland" and whose "goodbye" attribute has exactly
the value "Columbus":
span[hello="Cleveland"][goodbye="Columbus"] { color: blue; }
source: http://www.w3.org/TR/CSS21/selector.html#matching-attrs
but when I tried to validate it, I got this warning:
[hello="Cleveland"] and [goodbye="Columbus"] are incompatible
Thought, this selector is working on IE7, FF, Opera, Safari & probably
others.
Did I find a bug in the validator?
Thanks in advance,
Gilles

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