gdb does not step into sources of Qt 5.1.1 package

1. Create a new Qt GUI Application.
2. Set a breakpoint in the first line of main function:

   QApplication a(argc, argv);
   

3. Let the debugger run into the breakpoint.
4. Step into (F11).
   Creator still shows the same line.

Instead, Creator should step into qapplication.cpp. With my own out of source build of Qt stable 5.2, this works.