QClipboard setImage alpha black

[Talei]

Hello,
I stumbled upon a problem with QClipboard and image transparency.
What I want to do is to set into clipboard transparent image and paste it into Paint application. After setting it up and pasting alpha channel is black.

My test code:

@ QImage img = QImage(QSize(640, 480), QImage::Format_ARGB32);
img.fill( Qt::transparent);
QPainter p(&img);
p.fillRect( QRect( QPoint(10, 10), QSize(320, 240)), Qt::red);
p.end();

QApplication::clipboard()->setImage( img);@

Qt 5.3.2 MinGW - Win8.0

Any idea why alpha is black?

[Talei]

I tried with different combinations of mime etc. always alpha is black.
Any idea how to correct this?