lattice draw.key(): position of key in panels

-----Original Message-----
From: Vasiliev B at CEFCOM HQ at Ottawa-Hull 
Sent: Tuesday, 25, January, 2011 16:22 PM
To: 'r-help at r-project.org'
Subject: lattice draw.key(): position of key in panels

Good afternoon,

I am working on a plot that requires custom legends to be 
placed in some panels of the plot; other panels do not 
contain legends.  The problem that I run into is positioning 
of the legend in individual panels. In particular, the 'x' 
and 'y' elements of the key-list are ignored by draw.key() 
when it is called from inside a panel function.  As a result, 
the legend is placed in the middle of the panel.  The example 
below illustrates this problem.

df <- data.frame(x=c(1,1),y=c(1,2),type=c("A","B"))

panel.xyplot.x <- function(...) {
  # draw data
  panel.xyplot(...)

  # create key-list
  pnlid <- panel.number()
  lbl <- ifelse(pnlid==1,"AA","BB")
  pts <- Rows(trellis.par.get("superpose.symbol"),pnlid)
  key <- list(points=pts,text=list(lbl),x=0.1,y=0.9,corner=c(0,1))

  # draw key
  draw.key(key,draw=TRUE)
}

oltc <- xyplot(y~x|type,data=df,panel=panel.xyplot.x)
print(oltc)

I tried using 'vp=current.viewport()' in the call to 
draw.key() but it did not help.  Can anybody suggest the 
proper way to specify position of the key-list so that it is 
respected by draw.key() when called within a panel function?

Sincerely,
Boris Vasiliev.