[css3-borders] Should border-radius clip backgrounds in the presence of border-image?

When the "border styles" are suppressed due to the presence of a border
image, should browsers continue to clip the background to the specified
border-radius?  Empirically, both Firefox (3.5 and trunk) and Webkit
(1.1.10) do so, but I doubt anyone really thought about it.  I could
argue both ways on whether it's desirable -- the attached example looks
bad, but I could come up with a border image for which it would look
good.

zw