Thinking about this particular problem leads me back to the discussions of neutrals and 310.15(B)(4).
The neutral here is generally not considered a current carrying conductor.
But consider: if you had a 40A, 120V purely resistive load connected from phase A to neutral, and a 40A, 208V purely resistive load connected between phases A and B, you would end up with 40A on each conductor, including the neutral, with absolutely nothing wrong and purely resistive loads.
-Jon
