[css3-flexbox] Is painting order affected by 'flex-order'?

Issue link: http://wiki.csswg.org/topics/css3-flexbox-painting-order

The 'flex-order' property “reorders” flexbox items, allowing them to
display independently of their source order.

Does this reordering affect painting order? That is, given the following markup:

<flexbox> <a style=“flex-order:2;”>foo</a> <b
style=“flex-order:1;”>bar</b> </flexbox>

If the <b> child overlaps the <a> child, should it paint above (that
is, according to its source order) or below (according to its display
order)?

A. 'flex-order' affects the painting order - items moved earlier paint
underneath items moved later.

B. 'flex-order' has no effect on painting order - the original source
order determines whether things are painted above/below others.

WebKit's implementation chooses option A, and I think this is sanest -
as much as possible, the reordering should act exactly like it was
*always* in that order.

Thoughts?

~TJ