enhanced3D plot with or without mesh

Hi all,
I am just new on the list with the following puzzle:

trying this (a simple modification of the one at 
http://www.telefonica.net/web2/biomates/maxima/gpdraw/func3d/index.html)

load(draw)$
draw3d(enhanced3d   = true,
       palette      = gray,
       meshed_surface = false,
       surface_hide = true,
       explicit(20*exp(-x^2-y^2)-10,x,-3,3,y,-3,3),
       meshed_surface = false,
       explicit(x+y,x,-5,5,y,-5,5)) $

you get exactly the same plot of a plane intersecting a "witch hat".

However:
- set TRUE the mesh on the witch hat, and FALSE the mesh on the plane  ==> 
top half of hat disappears
- set FALSE the mesh on the witch hat, and FALSE the mesh on the plane  ==> 
top half of hat disappears
- set FALSE the mesh on the witch hat, and TRUE the mesh on the plane  ==> 
top half of hat barely visible (plane's mesh does not appear to be hidden 
behind the hat's surface)
- setting or unsetting surface_hide does not help with the disappearing of 
the top half of the witch hat

Otherwise I find the DRAW interface just great !

Anybody with suggestions ?

Thanks

Cheers

Luca