Thinks to check:

- loading of custom dumpers (as seen on QByteArray/QString)
- availability of Qt debug information (custom display of QObject derived
class)
- availabitily of Qt sources (single step into some Qt *._cpp_ file)
- setting of breakpoints on dynamically loaded plugins (try plugin.cpp here, especially in constructors)
- check I/O  (qDebug, std::cout, std::cerr)