When I have a diagram with multiple top nodes, and I'm laying it out left to right, the top row always center aligns the items. But in all other rows, it seems to be top aligned after each taller item. See how the box "Three" is center aligned in First Row. But in Second Row, the box "C" is not center aligned.
Here's an example in the playground:
http://jsplayground.syncfusion.com/eagzlgr2