QComboBox sizing does not consider new lines

#include <QApplication>
#include <QDialog>
#include <QHBoxLayout>
#include <QComboBox>
int main( int argc, char* argv[] )
{
    QApplication app( argc, argv );

    QDialog dlg;
    new QHBoxLayout( &dlg );

    for ( int i = 0; i != 5; ++i )
    {
        QComboBox* box = new QComboBox();
        box->addItem( "Hello World\nHello World\nHello World" );
        dlg.layout()->addWidget( box );
    }
    dlg.show();
    return app.exec();
}