MultiChart tooltip doesn't format header

I have a graph that displays formated dates on the X axis ('%Y %b') but when I hover the mouse, the tooltip doens't display the header with the date formated. By adding the code:

.headerFormatter(function(d, i) {
   return xAxis.tickFormat()(d, i);
})

To the tooltips, the problem got solved.

Thank you for making such a good graphics lib.