[Solved]-Odd Scale Change When Updating Chart Type-Highcharts

Workaround with swapping stacking property on render event:

chart: {
  type: 'bar',
  events: {
    render: function() {
      var chart = this,
        series = chart.series[0],
        options = chart.options,
        stacking = options.plotOptions.series.stacking;

      if (stacking === 'normal' && series.type === 'line') {
        chart.update({
          plotOptions: {
            series: {
              stacking: ''
            }
          }
        });
      } else if (stacking === '' && series.type === 'bar') {
        chart.update({
          plotOptions: {
            series: {
              stacking: 'normal'
            }
          }
        });
      }
    }
  }
}

Demo: https://jsfiddle.net/BlackLabel/hdL7eb9x/