R devel - Feb 2011 - sys.calls Behaviour

Hello,

I noticed a difference between S4 methods and ordinary methods for sys.calls(),
where it seems to report everything twice for S4 methods. This seems strange. Am
I overlooking something ?
> f <- function(x)
+ {
+ g(x)
+ }
> 
> g <- function(y)
+ {
+ cat(y, '\n')
+ sys.calls()
+ }
> 
> f(5)
5 
[[1]]
f(5)

[[2]]
g(x)
> 
> 
> setGeneric("conv", signature = c("x"),
function(x){standardGeneric("conv")})
[1] "conv"
> 
> setMethod("conv", "character", function(x)
+ {
+ conv(as.numeric(x))
+ })
[1] "conv"
> 
> setMethod("conv", "numeric", function(x)
+ {
+ cat(x, '\n')
+ sys.calls()
+ })
[1] "conv"
> 
> conv("5")
5 
[[1]]
conv("5")

[[2]]
conv("5")

[[3]]
conv(as.numeric(x))

[[4]]
conv(as.numeric(x))
> 
> sessionInfo()
R version 2.12.2 (2011-02-25)
Platform: i386-pc-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=English_Australia.1252  LC_CTYPE=English_Australia.1252   
LC_MONETARY=English_Australia.1252 LC_NUMERIC=C                      
LC_TIME=English_Australia.1252

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

--------------------------------------
Dario Strbenac
Research Assistant
Cancer Epigenetics
Garvan Institute of Medical Research
Darlinghurst NSW 2010
Australia