Strange Circle Pack Layout Drawing Order in Chrome vs Firefox

[brittanyk]

Hi,
I have been using the circle packing layout in protovis with ~100
circles. I am shading the circles such that the central one is the
darkest shade of blue and then the circles going outwards from it are
of decreasing transparency. To achieve this, I just sort the array of
data by descending transparency. When in firefox, the layout behaves
as expected and produces an image of decreasing transparency going
outwards. But when in chrome, I noticed that the central circle (seen
as the darkest shade of blue) gets shifted one position to the right
(where the second circle should be). The second circle gets placed
someplace random near the edge of the layout and the node in this
place becomes the centre. Basically, it makes my image look funny.
My question is, where should I start looking to debug this? Or has
anyone else ever had any similar chrome/firefox conflicts?

Much Appreciated,
Brittany