LumenRT - solar reflection on ground

I have a scene with a mapped ground layer.

For some reason, the sun reflects off this surface - even though it has no reflective or specular material attributes.

Is there any way I can switch the sun's visibility off (while retaining its presence for lighting and shadows)? Are there other material attributes I need to adjust?

I don't recall this happening in previous versions of LumenRT.

Thanks,

Max

LumenRT 16.14.60.67

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