g.drawImage(img, 0, 0, this);
is redirected to the DrawImage pipe (which I of course have not implemented until now ^^).
After all it quite puzzles me why there is a DrawImage-Pipe which seems to be able to handle all cases, and things like ScaledBlit and TransformedBlit. I registered a TransformedBlit which does does not seem not to be used in this case.
However the registered ScaledBlit does its job :)
Update: Seems to be done from inside OGLDrawImage. Did the same with XRDrawImage and now transformed blits also pick up the appropriate loops :)