Alpha channel influenced by a blend mask

Hi there,
I’m having a trouble with an alpha RE.

The pass seems to be influenced by the mask of the blend material of the ground.
It’s a common blend shader with a procedural map as a mask… nothing more.

But after opening it on PS, I get translucency on the ground…

Where does it come from ? I never had it before…

Thanks !

Jules (nemluvim Czecky French guy from EUE)