QTextToSpeech::volume() and pitch() always return 0

The QTextToSpeech::volume() and QTextToSpeech::pitch() always return 0, even after you changed them by setVolume() and setPitch()

I got this problem on openSUSE Tumbleweed, with speech-dispather and speak-ng as the backend.

And more, you can't determine whether the backend is started via state() and stateChanged() ! It seems that QTextToSpeech do not emit the stateChanged() signal.