Phonon cannot stream media (mp3) via cellular Network (GPRS)

I cannot playback an mp3 stream from the network over cellular network (GPRS, UMTS). Over WLAN it works.
Phonon always tries to connect to an WLAN network. If no WLAN is available, it gives an error (symbian -39). I try to set the connection to my mobile operator with QNetworkSession. In my opinion this session should be used for all connections done in the application. But this session is only used by QNetworkAccessManager, phonon player still tries to connect to WLAN.

1. What did you do?
Create a new Session to Mobile network Operator with QNetworkSession. Try to download an xml file with QNetworkAccessManager and display it. Then try to open an mp3 stream with phonon player.
First tried it with WLAN connection. Then tried it without WLAN connection, but GPRS/UMTS connection.
2. What did you expect to happen?
XML is displayed correctly and sound of mp3 stream is hearable.
3. What happened instead?
WLAN Connection: XML is displayed correctly, mp3 stream is hearable correctly
GPRS/UMTS Connection: XML is displayed correctly, mp3 stream is not hearable. Error -39 is thrown instead.