warning on gamma option in par(args) or calling par(= new)?

Dear All,

I have the following function

tstpar <-
 function(n = 200, want.pdf = FALSE, pdfFileName = NULL){
   oldpar <- par(no.readonly = TRUE)
   on.exit(par(oldpar))
   steps  <- seq(from = 1, to = 8, by = 1)
   h <- 10; w <- 6
   if(want.pdf){pdf(file = pdfFileName, onefile = TRUE,
   paper = "letter", width = w, height = h)}
   par(mfrow = c(4,2))
   for(i in steps){
     txt <- paste("i = ", i)
     hist(rnorm(n), main = txt)
   }
   if(want.pdf){dev.off()}
 }

when called with default values tstpar() every thing works fine.
However I get 2 sorts of warnings
1- if I call the function to generate a pdf as
  tstpar(want.pdf = TRUE, pdfFilename = "jj.pdf")
  I get the following warning msg:
  calling par(new=) with no plot in: par(oldpar)
  with an empty device which I don not understand since I close
  the device in the function.
2- If I comment the line
  if (want.pdf){dev.off()}
  I get the following warning
  'gamma' cannot be modified on this device in: par(args)
  with 2 empty devices.

I do not understand why I get those warnings and why I get those empty devices.
I looked up in RSiteSearch and I found the 2 following posts
http://finzi.psych.upenn.edu/R/Rhelp02a/archive/38553.html
In this post M. Schwarz explains that there is not a plot created that's why R generates the
warning. In the case of tstpar, I generate the hist plots and should not be getting the warning.

And in the following post Prof Ripley refers to an old R warning for pdf() devices
Which is not the case here.
http://finzi.psych.upenn.edu/R/Rhelp02a/archive/23215.html

I do not see what I am missing. Thanks for any hint.
I use R 2.5.1 under Win XP.
I apologize if the question is related to my older R version which I will upgrade.

AA.

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