I have never had problems with masked textures, but alpha'ed entities (both in texture and brush level) have always been problematic. And it isn't Blitz' fault either...
On a side note:
The only company, to my knowledge, that have ever produce a hardware accelerated 3D card that handles alpha without any problems is PowerVR/Imagination Technologies.
On a side note:
The only company, to my knowledge, that have ever produce a hardware accelerated 3D card that handles alpha without any problems is PowerVR/Imagination Technologies.