[css3-background] percentages in border-radius - really relative to height?

I see that the latest revision of the border-radius spec
[ http://dev.w3.org/csswg/css3-background/#the-border-radius ] allows
<percentage>s as well as <length>s - this is nice, since Mozilla has had
that as an extension for some time.

However, it says

# Percentages for the horizontal radius refer to the width of the
# border box, whereas percentages for the vertical radius refer to the
# height of the border box. 

Mozilla currently treats percentages for either radius as relative to
the width of the border box.  This is partially a hold-over from when
Mozilla only implemented quarter-circle border curves, and I'm not
totally opposed to changing it.  However, I think

 border-top-right-radius: 10%

should always produce a quarter-circle, which it would not do if the
vertical axis were relative to height.  And I think it would be
confusing if that value and "10% 10%" were not interchangeable.  So I
ask the committee to reconsider the behavior.

If this particular argument was already considered and rejected, I
would appreciate a pointer to the discussion.

zw