warning: "using absolute and relative lengths in margin"

For URI : http://www.desktoppublishingforum.com/dtpfor_2.css I 
received this warning for two margin settings:

>>  Line : nn (Level : 2) You have some absolute and relative lengths 
>>in margin. This is not a robust style sheet. <<

This is what the two lines had:

	>> margin: 0 3% 0 0;

	>> margin: 0 0 0 3%;

I changed the first one to:

	>> margin: 0% 3% 0% 0%;

And re-ran the validation. This time I received a warning for only 
the second line.

I have quite a few properties that use zero with no value; the 
warning is given only for lines with 0 and another value expressed as 
%.

Surely, there should not be any warning when absolute lengths are set 
to zero. This must be a bug in the validator, no?