http://bugs.winehq.org/show_bug.cgi?id=5730
------- Additional Comments From gbrammer@gmx.de 2006-18-12 15:00 ------- Was fixed in commit 3c5b9557b548a122a7375cf199b4a9b242506115 "ddraw: Fix IDirectDrawSurfaceImpl_SetColorKey to also change surface_desc."
The Problem was that SetColorKey did not change the surface description (only the underlying WineD3D surface), so GetColorKey returned the old value, which Baldur's Gate used to draw the transparent portions of the sprites. The actual blitting was done with the correct color key.