Why QTreeView only expands on doubleclicks on some of the columns?

jerrry94087

I have QTreeView with data supplied with QItemSelectionModel with 2 columns.
These were called from the tree constructor:
setSelectionBehavior(QAbstractItemView::SelectRows);
setSelectionMode(QAbstractItemView::SingleSelection);
setDragDropMode(QAbstractItemView::NoDragDrop);
setExpandsOnDoubleClick(true);

But for some reason only doubleclicks on the first column expand the items. And doubleclicks on the second columns do nothing.
How can I understand why doubleclicks on the second column don't expand the items in the tree?