flow() not connecting the dots

Hi, there is another glitch when flowing only one of two XY lines at a time. In this case, it won't render the lines between the dots:
http://jsfiddle.net/muf8voq9/
Also, this fiddle places dots wrong since it's not a timeseries, which is #423.
My use case is a live updated timeseries, so I could do this by keeping the data somewhere else and calling load(), but then I run into issue #906, which makes it look odd.