QMessageBox can not be closed/dismissed on touch phones if any widget is fullscreen

The problem is that any fullscreen widget will cause the softkeys to be hidden, and on touch phones, this means they are also not clickable.

This program demonstrates the problem:

int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    QWidget w;
    w.showFullScreen();
    QMessageBox::information(&w, "Hello", "World");
    return app.exec();
}

There are several ways one could fix this:
1. Don't use softkeys when a widget is fullscreen. Use the default Qt buttons instead.
2. Make the softkeys reappear when the currently focused widget is not a fullscreen widget.