WebKit, FF and the rest suffer from FOUT; we cope with it by hiding and monitoring the SVG .getBBox() call return values as those are what's important to us: see the WARNING comments in the code.
Mouseover any stream strip when you just updated and the update transition will halt, so that you're still stuck with the 'old' data. Click 'update' twice more, not moving the mouse outside the button, to recover. (Yes, all streamgraph examples in github / gist suffer from this AFAICT. Haven't investigated a fix, yet.)
Use / Play
Hover over the stream strips, the legenda and see the fades; click on either of 'em to highlight one or more streams. Hit the
button to switch between the two datasets.