Skipping panels in Lattice

Dear all,

I wish to generate a lattice boxplot which skips an empty cell in a
design. I have trawled r-help, scruitinized xyplot(lattice) help
page, and merrily reproduced examples of using skip from a couple of
previous r-help queries and the example given in Pinheiro & Bates.
But I must be missing something...

Here's an example (running R 1.9.1 on Win2k):

# generate some data

df1 <- data.frame(expand.grid(obsnum=seq(1, 15, 1), faca=c("A1",
"A2", "A3"), facb=c("B1","B2", "B3", "B4"), facc=c("C1","C2")),
dv=rpois(15*3*4*2,10))

# now get rid of the cell B4 & C1 to simulate a missing treatment
combination

df2 <- df1[df1$facb !="B4" | df1$facc !="C1", ]

# plain vanilla lattice plot generates an empty panel corresponding
to the empty cell

plot1 <- bwplot( dv ~ faca | facb*facc, data=df2)
plot1

# now try to skip the empty panel

# turn plot history on so that the separate pages can be recalled

plot2 <- update(plot1, skip=c(rep(F, 3), T, rep(F, 4)))
plot2

and the 4th panel position of the bottom row is skipped, BUT the
B4&C1 cell is shunted to the top left of row 1 and the last panel of
plot1 is now moved to page 2. Messing with layout= doesn't help,
neither does substituting NA for the values of the missing cell
(instead of cutting it out of the data frame). I also get the same
behaviour for stripplot and dotplot too.

Apologies if I've missed a previous solution to this during my
searches of the archive.

Regards,

Leon Barmuta
School of Zoology & TAFI, University of Tasmania, Australia.