Phonon: multiple instances of AudioOutput, setVolume(qreal) doesn't work properly

[willypuzzle]

I have a program where I have multiple different instances of AudioOutput class,
but setVolume(qreal) method works properly only with the last instance.
With other instances it does nothing.
Why?
What could I do?

NOTE:
Sounds and musics outputs normally ....
I have tried to create a path between different instances of Phonon::MediaObject and the same AudioOutput object (in order to have only one instance of AudioOutput class) but it doesn't work.

I thought it could be a bug ....

[kripton]

I've got the same problem:
https://bugs.kde.org/show_bug.cgi?id=321172