code: function setInvert() {			
  			var size = {
  				width: series.yAxis.len,
  				height: series.xAxis.len
  			};
  			
  			each(['group', 'markerGroup'], function (groupName) {
  				if (series[groupName]) {
  					series[groupName].attr(size).invert();
  				}
  			});
  		}
docs: A fixed size is needed for inversion to work