alpha = 0 isn't transparent

OK, I’m stumped.
I have done this several times before, not sure what’s happening here/now.
I have two materials, who are identical but with separate material IPOs. One fades in from alpha=0 to 1, the other fades out a=1 to 0. Simple, right? Well the Mat preview render sphere doesn’t show it properly for either material.
There are no textures affecting Alpha. (I tried with all textures cleared out anyway…just to try).
ZTransp is ON. (TraSha is on…tried it off too).
NO Ramp shaders.
NO funnyness…just a fairly plain material with two proc textures (one’s a stencil, the other’s affecting NOR).
AO is on (standard Ray Trace) - I tried with it off too…same result, but without the shading.
Not using Sun/Sky.
Using build 14000 SVN, but also tried with stable 2.45. (Win XP Pro 32bit Intel computer)
Check out the render:

Scene has one Sun, no extra Ambient Light, using BI renderer.
I say “Tile material” but I’m not using the new tile Tex plugin. It’s just cause it’s a roof tile.
I’ll leave it for now and go on with the rest of the scene, time is ticking…
Thanks for any ideas…

color <> alpha. put something behind an alpha 0 and you will see it. if there is nothing behind it, the color that you see will be the color of the object. click and drag over the render window and you will see that the roof is indeed alpha 0.

but I’ve done this before…in this same scene. It works as expected.
The cube is always in the scene…the only thing changing is the alpha. This set up is the same - one sun light, ray tracing, Ray-AO (for second half). TraShad for plane and Cube.

The scene in #1 has cement tiles on top of wood strapping on top of the underlay on top of plywood. just like a real roof. The Piles of Tiles are fading out as the fully tiled roof fades in. But they are not showing as fully transparent, as they should at the appropriate times.

dschnell, try setting specular to zero. If that doesn’t work, any chance you could post the blend?

can’t post the blend…I’d have to strip it down.
spec=0 didn’t change much at all.
I’m just going to leave it I think…unless I have an epiphany. (or someone else does). I’ll probably try to rebuild the material from scratch…see what happens. time is running short though (It will be a late night tonight). I think I’ll be hiring ResPower for rendering…4000ish frames…the last 1000 or so are almost 3min/ea on an OC q6600. (2.95/core).