QGridLayout does not allocate sufficient space to all widgets if it has one widget with setMaximumWidth property.

#include <QtGui>


int main(int argc, char** argv)
{
    QApplication app(argc, argv);
    QWidget widget;
    QGridLayout grid(&widget);
    QHBoxLayout hbox;
    hbox.addWidget(new QRadioButton("Button one", &widget));
    hbox.addWidget(new QRadioButton("Button two", &widget));
    hbox.addWidget(new QRadioButton("Button three", &widget));

    grid.addLayout(&hbox, 0, 0,1,6);// with this combo box is not fully shown
    //grid.addLayout(&hbox, 0, 0); // with this there is huge space between line edit and labels

    QLineEdit* edit(new QLineEdit(&widget));
    edit->setMaximumWidth(40);
    grid.addWidget(edit, 1, 0);
    grid.addWidget(new QLabel("A", &widget), 1, 1);
    grid.addWidget(new QLabel("B", &widget), 1, 2);
    grid.addWidget(new QLabel("C", &widget), 1, 3);
    grid.addWidget(new QLabel("D", &widget), 1, 4);
    grid.addWidget(new QLabel("E", &widget), 1, 5);

    widget.show();
    return app.exec();
}