I know I've certainly had alot of trouble with the Alphablending stuff.
I remember looking for some equivalent in GDIPlus (even a
non-native/slow one), but never finding one. I do remember changing the
bit depth of the screen made all the difference, as well as changing the
level of hardware acceleration in the "Troubleshooting" tab of the
Advanced graphics settings under Display properties.
There appears to be no useful equivalent that works under Windows. It
might have something to do with the way we render images using tiff/etc.