http://bugs.winehq.org/show_bug.cgi?id=22958
--- Comment #3 from Vincent Povirk madewokherd@gmail.com 2010-06-08 15:26:00 --- If gdiplus cares about the alpha channel of a 32-bit image, it should be writing the image data directly rather than using gdi32 to draw it. Unfortunately, that doesn't always happen currently.
If this ever worked, it was by coincidence.