Phonon::VideoWidget return inconstant sizeHint() under macosx 10.8

I have an application with a successfully embedded a Phonon::QVideoWidget in a QGraphicsItem. This application is based on QT 4.7.x (x from 0 to 4). It works well under Linux (...), windows (XP, seven, 8) and Mac OS X (from 10.6.x -> 10.8.x)

I recently found a strange behavior under Mac OS X 10.8 with Phonon video widget initial size: video size hint is twice as big as it should be.

I have two physical system running Mac Os X 10.8.2 :
-iMac 27" (no problem)
-MacBookPro 15" "Retina" (with problem)

Circumstances : I use virtual method QWidget::sizeHint(), called from a Phonon::VideoWidget object, to retrieve video Height and Width.
And obviously, I wait for "Phonon::LoadingState" state to fall in "StoppedState" before doing that.
It works well on every system we tested (linux, windows, mac os x) except on that MacBook pro Retina running mac os x 10.8.2.

I tryed to debug deeply in phonon qt7 sub component and found something suspicious.

This routine is use to retrieve initial video size under phonon/qt7 at least since qt 4.7:

 
QRect QuickTimeVideoPlayer::videoRect() const
{
    if (!m_QTMovie)
        return QRect();

	PhononAutoReleasePool pool;
    NSSize size = [[m_QTMovie attributeForKey:@"QTMovieCurrentSizeAttribute"] sizeValue];
    return QRect(0, 0, size.width, size.height);
}

After investigating "QTMovieCurrentSizeAttribute" usage, I found that it might be deprecated or not applicable under some circumstances.
I also found that Apple introduced new QTMovie attributes to retrieve "strange kind of" sizes from a movie. Especially an undocumented attribute, named
"QTMoviePreferredTransformAttribute" that seems to have the ability to unexpectedly scale videos.
Here is the only usage of this attribute I use to found (at http://opensource.apple.com/source/WebCore/WebCore-955.66/platform/graphics/mac/MediaPlayerPrivateQTKit.mm) :

 
void MediaPlayerPrivate::cacheMovieScale()
{
    NSSize initialSize = NSZeroSize;
    NSSize naturalSize = [[m_qtMovie.get() attributeForKey:QTMovieNaturalSizeAttribute] sizeValue];

#if !defined(BUILDING_ON_TIGER) && !defined(BUILDING_ON_LEOPARD)
    // QTMovieCurrentSizeAttribute is not allowed with instances of QTMovie that have been 
    // opened with QTMovieOpenForPlaybackAttribute, so ask for the display transform attribute instead.
    NSAffineTransform *displayTransform = [m_qtMovie.get() attributeForKey:@"QTMoviePreferredTransformAttribute"];
    if (displayTransform)
        initialSize = [displayTransform transformSize:naturalSize];
    else {
        initialSize.width = naturalSize.width;
        initialSize.height = naturalSize.height;
    }
#else
    initialSize = [[m_qtMovie.get() attributeForKey:QTMovieCurrentSizeAttribute] sizeValue];
#endif

    if (naturalSize.width)
        m_scaleFactor.setWidth(initialSize.width / naturalSize.width);
    if (naturalSize.height)
        m_scaleFactor.setHeight(initialSize.height / naturalSize.height);
}

This piece of code introduce a possible scale factor between the "natural" size of a movie and its "initial" size. And this seems to be the explanation of the issue I observed.
I'm not sure to really understand Apple motivation to scale video "real" size, nor if its a bug or an "Apple feature", but I can see its disastrous effect on phonon video widget embedded in a QGraphicScene (scale and position side effects).

I think this bug (if any) is still there in Qt 4.8 (and more ?) because QuickTimeVideoPlayer::videoRect() still has the same implementation. (from http://qt.gitorious.org)

And I would appreciate any advice from a qtPhonon developer.