Hi Henri,
I was playing with camdraw restrictions lately and there was an ALM interaction that surprised me.
The camdraw spheres seem to be interacting with more than just the diffuse texture layers.
With camdraw on, it looks like the spheres and surroundings have a high specular/environment setting, and you don't see this behavior with ALM off.
When switching ALM on and ALM off with camdraw active, you can quickly see the difference.
I have included some code you can just drop in a prim so you can see the settings I used, toggle them on and off, and see if this reproduces itself for you.
I am not sure if this is expected behavior or not, since I have never used anything but solid black before, but it seemed worthy of mention.
Thanks!
~Lycia