code: function (e) {
  		var chart = this.chart,
  			chartPosition = this.chartPosition,
  			hoverSeries = chart.hoverSeries;
  
  		e = this.normalize(e, chartPosition);
  
  		// If we're outside, hide the tooltip
  		if (chartPosition && hoverSeries && !this.inClass(e.target, 'highcharts-tracker') &&
  				!chart.isInsidePlot(e.chartX - chart.plotLeft, e.chartY - chart.plotTop)) {
  			this.reset();
  		}
  	}
docs: Special handler for mouse move that will hide the tooltip when the mouse leaves the plotarea.
  Issue #149 workaround. The mouseleave event does not always fire.