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http://lists.w3.org/Archives/Public/www-style/2009Dec/0252.html
I think I addressed this. The spec now has "If property is not specified for a keyframe, or is specified but invalid, the animation of that property proceeds as if that keyframe did not exist. Conceptually, it is as if a set of keyframes is constructed for each property that is present in any of the keyframes, and an animation is run independently for each one."
*** This bug has been marked as a duplicate of bug 14636 ***