Bug Report: CSS3 Validation of "ch" unit

When set to CSS3, the CSS Validator states:

    Value Error : min-width
    <http://jigsaw.w3.org/css-validator/nullvisudet.html#propdef-min-width>
    Unknown dimension 15ch

While the CSS3 Values and Units <http://www.w3.org/TR/css3-values/> 
draft specification states <http://www.w3.org/TR/css3-values/#relative0>:

    ch:  The width of the "0" (ZERO, U+0030) glyph found in the font for
    the font size used to render. If the "0" glyph is not found in the
    font, the average character width may be used. How is the "average
    character width" found?

The Validator should mark "ch" as a valid unit when set to CSS3.  The 
same error occurs in the development version 
(http://qa-dev.w3.org:8001/css-validator/).