vray 5 frame buffer not saving reflections on matte object plane

[3dDogCatLizard]

Hi, I used to be able to render just the reflections on a plane with a scene. The frame buffer shows the reflection but when I save it as png or exr, the reflections will not save.

The plane Vray Properties
Matte Object > On
Matte for refl/refr > On
Alpha Contribution -1.0

The plane VraymtlWrapper settings
Matte Surface > On
Alpha Contribution > -1.0
Matte for refl/refr > On

On the previous version of vray frame buffer, I can save it directly into a png file.

Appreciate the help, thanks