Unwanted alpha channel behavior

[PerFotoVDB]

Hi all,

I am getting some real strange behavior when rendering to psd 16-bit with alpha.
In the image you can see on the left normal alpha behavior as this is the background.
On the right you have geometry with holes in it. Behind this geo is a mesh structure with created with an advanced material on a plane.
Behind this mesh is the inside of a loudspeaker (can't show because of nda).

The material of the mesh is based on an advanced material with a procedural weave (see screenshot) and has no map in its opacity slot.

Why does the render show alpha behind the geo?

Thanks for the help,
Per