http://bugs.winehq.org/show_bug.cgi?id=30721
--- Comment #2 from Vincent Povirk madewokherd@gmail.com 2012-09-25 16:19:25 CDT --- I'm getting the same results in my testing on Windows - GetColorContexts for a BMP frame returns WINCODEC_ERR_UNSUPPORTEDOPERATION.
The PNG decoder succeeds and returns 0 contexts for all the images I've tried. Maybe WPA has some builtin knowledge of which decoders implement this?