Nested QWidgets break layout baseline

#include <QApplication>
#include <QComboBox>
#include <QHBoxLayout>
#include <QLineEdit>
#include <QPushButton>
#include <QVBoxLayout>

template<typename T>
QHBoxLayout *addRow()
{
    auto widget = new QWidget;
    auto layout = new QHBoxLayout;
    auto control = new T;
    layout->setContentsMargins(0, 0, 0, 0);
    layout->addWidget(control);
    layout->addWidget(new QPushButton("Push"));
    widget->setLayout(layout);

    auto row = new QHBoxLayout;
    row->setContentsMargins(0, 0, 0, 0);
    row->addWidget(new QPushButton("Push"));
    row->addWidget(widget);
    row->addWidget(new QPushButton("Push"));
    return row;
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QWidget mainWidget;
    auto vlayout = new QVBoxLayout;
    mainWidget.setLayout(vlayout);

    vlayout->addLayout(addRow<QLineEdit>());
    vlayout->addLayout(addRow<QComboBox>());

    mainWidget.show();
    return a.exec();
}