The clicked() signal for the QPieSlice cannot be emitted

If you add connect(slice,&QPieSlice::clicked,[]()->void{qDebug("clicked");}); before connect(slice, SIGNAL(hovered(bool)), this, SLOT(explodeSlice(bool))); in the nested donuts example http://doc.qt.io/qt-5/qtcharts-nesteddonuts-example.html, the clicked() signals cannot be emitted except the QpieSlices in the last added QPieSerie, same behaviour can be gotten when calling pressed(), doubleClicked(), or these signals of QPieSeries. It seems only the hovered() signal can work well.