Dates in tooltips are wrong when localtime = false on timeseries chart

If you look at this fiddle: http://jsfiddle.net/26m1w5tj/ you'll see that the date indicated in the tooltip does not match the date on the x-axis. Remove the `localtime: false` and the date on the x-axis ticks changes, but the date in the tooltip for the same positions along the chart remains the same. The date on the tooltip and the date on the x-axis should remain in sync regardless of the `localtime` settting.