C3: Spline chart drawing incorrectly

I am having sporadic issues with spline chart series. The series are drawing incorrectly. When I have two dates one after another, sometimes the line will loop over itself or the line will shoot past the next data point and then curve back instead of just curving directly to the next point. I think the drawing logic is incorrect. If I change the chart to be a "line" series instead it shows correctly.

You can see my issue if you copy the chart code into your example page. (http://c3js.org/samples/chart_spline.html)

Chart code example:
var chart = c3.generate({
data: {
x: 'date',
columns: [
['date',744336000000,752112000000,876096000000,882057600000,884304000000,888969600000,893203200000,897350400000,902361600000,908236800000],
['values',12.15,11.7,11.75,11.86,11.97,12.05,11.27,12.2,12.34,12.27]
],
type: 'spline'
}
});

Screenshot: