Possible to create multiple QStackedBarSeries on a single QChart?

[oracle3001]

I was wondering if it is possible to create two sets of QStackedBarSeries on a single QChart.

When I try to create two QStackedBarSeries and add them both to the chart in the usual way, I find that for each x, QT bars the two stacked bars over one another i.e.

// series 1
	QStackedBarSeries *series = new QStackedBarSeries();
	series->setName("Orginal Costs");
        int first = 0;
	int count = _n_meshes ;
	QVBarModelMapper *mapper = new QVBarModelMapper(this);
	mapper->setFirstBarSetColumn(0);
	mapper->setLastBarSetColumn(2);
	mapper->setFirstRow(first);
	mapper->setRowCount(count);
	mapper->setSeries(series);
	mapper->setModel(original_cost_summary_model);

// series 2
	QStackedBarSeries *series2 = new QStackedBarSeries();
	series2->setName("Optimized Costs");
	//int first = 0;
	//int count = _n_meshes;
	QVBarModelMapper *mapper2 = new QVBarModelMapper(this);
	mapper2->setFirstBarSetColumn(0);
	mapper2->setLastBarSetColumn(2);
	mapper2->setFirstRow(first);
	mapper2->setRowCount(count);
	mapper2->setSeries(series2);
	mapper2->setModel(final_cost_summary_model);

	chart->addSeries(series);
	chart->addSeries(series2);

Am I just missing something simple?