mental ray opacity map with hair and fur

I have a student doing a project with an outdoor scene.  The grass on the ground
is done with hair and fur.  There are some leafy plants done with simple
geometry that have Opacity maps applied. In mental ray where the shadows should
be on the grass surface  there  is simply a washed out area that has the  shape
of the simple geometry.  The first thing I noticed was that he was using a
default Opacity map.  I switched to a mental ray opacity map and  the shadows
were fixed up  fine.  However in areas that should be transparent on the leaf
surface, the rendering of the hair beneath has the same washed out flat quality.
 Have I failed to set up the Opacity map  correctly or is there a compatibility
problem between the hair and fur modifier an