Bug in handling of promises?

I'm working on a function that does adaptive sampling, and I thought
it would be handy to return the function's environment as part of the
result so that I could re-use local variables in a subsequent run.  My
first try didn't work, and it came down to code like this:

f <- function( H, prevEnv = NULL) {

+     if (!is.null(prevEnv)) H <- prevEnv$H
+     cat('Evaluate H to get ', H(1), '\n')
+     return(environment(NULL))
+ }

I thought that evaluating H would force it, so that H would be
available in the environment returned by the function.  But this is
not so:

env <- f( function(x) x^2 )

Evaluate H to get  1

env$H

<promise: 012094D8>

env$H(1)

Error: attempt to apply non-function

So I tried to explicitly force it:

g <- function( H, prevEnv = NULL) {

+     if (!is.null(prevEnv)) H <- prevEnv$H
+     force(H)
+     return(environment(NULL))
+ }

but this still doesn't work:

env <- g( function(x) x^2 )
env$H

<promise: 01206FC0>

env$H(1)

Error: attempt to apply non-function

It seems that I need to do an assignment to convert H from a promise
to an evaluated object:

h <- function( H, prevEnv = NULL) {

+     if (!is.null(prevEnv)) H <- prevEnv$H
+     H <- H
+     return(environment(NULL))
+ }

env <- h( function(x) x^2 )
env$H

function(x) x^2

env$H(1)

[1] 1

Is this a bug, or just the way things are?

I get the same results in both R-patched and R-devel.