NextMethod problem

Can anyone shed any light on what is going wrong here?
Its based on simplifying some actual code that exists in
model.frame.default.  It looks like a bug to me.  Thanks.

data(iris)

f.default <- function(x, subset, ...) {
 subset <- eval(substitute(subset), iris, .GlobalEnv)
 subset
}

# This one is ok
f(1, 1:3)

# putting an intermediate f.numeric in results in body
# of subset function being returned
f.numeric <- function(x, subset, ...) NextMethod("f")
f(1, 1:3)

# slightly different f.numeric results in error
f.numeric <- function(x, ...) NextMethod("f")
f(1, 1:3)

R.version.string # Windows XP

---

Output:

function(x, ...) UseMethod("f")
data(iris)

f.default <- function(x, subset, ...) {

+   subset <- eval(substitute(subset), iris, .GlobalEnv)
+   subset
+ }

# This one is ok
f(1, 1:3)

[1] 1 2 3

# putting an intermediate f.numeric in results in body
# of subset function being returned
f.numeric <- function(x, subset, ...) NextMethod("f")
f(1, 1:3)

function (x, ...)
UseMethod("subset")
<environment: namespace:base>

# slightly different f.numeric results in error
f.numeric <- function(x, ...) NextMethod("f")
f(1, 1:3)

Error in eval(expr, envir, enclos) : ..1 used in an incorrect context,
no ... to look in

R.version.string # Windows XP

[1] "R version 2.1.0, 2005-04-18"