(fixed) Magic doors with Alpha don't fade correctly

[Gambit37]

Magic doors fade in and out in DSB. However, If I use an animated bitmap with alpha transparency as a magic door, the fading goes very ugly and turns into lots of kaleidoscopic pixels.
Here's images of the door and then what happens when it starts to fade:

EDIT: Image removed, no longer available

[Sophia]

That dissolve transition must be doing funny things to the alpha channel.
I'll sort it out.