'rowSpan' in QGridLayout::addWidget() can't be -1 when 'row' is the last row

One aspect of void QGridLayout::addLayout(QLayout * layout, int row, int column, int rowSpan, int columnSpan, Qt::Alignment alignment = 0) is described as "If rowSpan and/or columnSpan is -1, then the layout will extend to the bottom and/or right edge, respectively." in Qt Assitant.

However, it turns out I can NOT set rowSpan to -1 when row>0 (and that is ,you can ONLY set rowSpan to -1 when row=0, same to column/columnSpan), or the debugger would give error "ASSERT failure in QVector<T>::at: "index out of range", file ..\..\include/QtCore/../../src/corelib/tools/qvector.h, line 350".

maybe a bug, maybe just need more explaination and notes in Assistant.