trees with opacity maps facing glass facade PROBLEMS

[pengo]

strange opacity problem

In this test image is visible the problem where the plane of the trees go over the glass wall in camera view, if watched better are visible the shapes of the planes geometries i used for the trees.

Why this poblem?

the forest planes has vray material applied with map on diffuse and opacity channels I tryed with unchecked 2 sided in vray materials but nothing better.

could someone explain how to avoid it

thanks in advance