[REG Qt 4.8.7 -> Qt 5.3.1] QToolTip not shown after showing QLabel

1. Build and run this simple program:

   #include <QApplication>
   #include <QLabel>
   #include <QToolTip>
   
   int main(int argc, char *argv[])
   {
       QApplication app(argc, argv);
       QLabel l;
       l.resize(300, 300);
   //    l.show();
       QToolTip::showText(QPoint(100, 100), "TT");
       app.exec();
   }
   

   It will just show the QToolTip.

2. Now uncomment the line l.show();, build and run the project again.
   Now the QLabel will be shown, but the QToolTip won't be shown anymore. There are no warnings or error messages.

Both, the QLabel and the QToolTip should be shown. With Qt 4.8.7, this works correctly.