[css3-flexbox]ordinal group and drawing order

Should flexbox items be drawn in source order or ordinal order?

The two implementations disagree (see attached test). If stacking context spec is unchanged, it has to be in source order. It makes more sense to me thought that drawing order is rearranged by ordinal...

Same question will eventually apply to grid or template layout, where coming up with an order different from source order can be quite complicated, which would be an argument in favor of source order.

What do you think is the right to do here?