drawing order in spplot

Many thanks to everyone involved in putting together the excelent sp 
package. I have just used for teaching a brief intro to applied geostats 
with gstat. Students found life much easier than a year ago when I had 
to try to explain a less structured approach to the data.
A simple question arose after the class. According to the spplot 
documentation "for grids and polygons sp.layout is drawn afterwards (so 
the item will not be overdrawn by the grid and/or polygon)".
So in this example we expected a DEM to be drawn first, then municipal 
boundaries.

 > class(municipios)
[1] "SpatialPolygonsDataFrame"
 > class(chisgrid)
[1] "SpatialPixelsDataFrame"

municips <- list("sp.polygons", municipios)
spplot(chisgrid["dem"],sp.layout=municips)

The municipal boundaries are drawn first then overdrawn by the DEM, 
which was not what we expected or wanted. I couldn't find how to avoid 
this, apart from the simple solution of ..

image(chisgrid,col=terrain.colors(20))
plot(municipios,add=T)

instead of spplot.The figures on  http://r-spatial.sourceforge.net all 
appear to have the grid drawn first. Is there a way to reverse this?

Duncan

Dr Duncan Golicher
Ecologia y Sistematica Terrestre
Conservaci?n de la Biodiversidad
El Colegio de la Frontera Sur
San Cristobal de Las Casas, 
Chiapas, Mexico

Email: dgoliche at sclc.ecosur.mx 

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