03-lines chart - tooltip showing on all lines

Hello!
I just created a 03-line chart, however, when using the method setTooltip(index, callback function, line), it doesnt works. I have done the following:

      myChart.setTooltip([arrayLinhaMedicao[indexMedicao][0], function(){this.alert('callback');}, 'linhaMedicao']);

The graph is generated without problems, but the "CallBack" function is not called properly. Actually, it turns into HTML link! When I DO NOT use the 03 parameter(to inform the line I want the tooltips), it works fine(javascript is executed without any issues), but I need the tooltip only in the central line, not at all lines. Can someone advise?

Thanks in advance,
Vinicius
vbatista[at]gmail[dot]com