phonon doesn't reproduce audio/video stream

Development machine: Linux Ubuntu 9.10 Qt 4.6-beta1 from a PPA(Personal Package Archive: https://launchpad.net/~mapopa/+archive/qt4.6)

Before installing Qt4.6 I was compiling and running (using Qt 4.5.3) without problems a simple application
using phonon to reproduce 2 independet audio video streams.
The same application, after the upgrading to Qt 4.6-beta1 (using the package from an Ubuntu maintainer)
doesn't reproduce the audio / video streams but the application doesn't crash and can terminate correctly (exit status 0).
Before to recompile I ran again the sequence: make distclean; qmake -project; qmake and make.