Wrong variable scope when callGeneric with dots argument is called by a generic that is called from another function

callGeneric-dots-bug.R

setGeneric("f1", signature=c("a"),
           function(..., a) standardGeneric("f1"))
setMethod("f1", c(a="ANY"), function(..., a) list(a=a, ...))
setMethod("f1", c(a="missing"), function(..., a) callGeneric(a=1, ...))
f2 <- function(b,c,d, a) {
    if (missing(a))
        f1(b=b, c=c, d=d)
    else
        f1(a=a, b=b, c=c, d=d)
}

## Neither of these calls triggers the callGeneric
f1(2,3,4, a=1)
f2(2,3,4, a=1)
## This triggers the callGeneric, but doesn't trigger the bug because we are calling f1 directly
f1(2,3,4)
## This triggers the callGeneric with f2 calling f1, so it triggers the bug
f2(2,3,4)