Can i use nnml as mail archive method?

Can i use nnml as mail archive method?

[Tang Yan]

I don't know where to find help and the problem is so strange.

I want to use nnml as mail archive method in gnus 5.10.6.

And what i have done is as follows:
------------------------------------
(setq gnus-message-archive-method
'(nnml "archive"
(nnml-directory "~/Mail/archive")
(nnml-active-file "~/Mail/archive/active")
(nnml-get-new-mail nil)))

(setq gnus-message-archive-group (concat "sent-" (format-time-string
"%m.%Y")))
------------------------------------
Just substitute `nnfolder' of the example in gnus info with `nnml'.

But something strange happens.

Then I exit gnus and emacs, delete `newsrc.eld' and `newsrc'(to ensure
no former results), re-enter gnus, send a mail, and exit gnus.

When I enter gnus the third time, I get a new group `sent-08.2004' and
a number `1' indicates there is a sent mail in it. But I cannot enter
the group. What's the worse, in minibuffer, the error message is:
cannot select _nnfolder_ group

And I exit gnus, open the file `newsrc.eld', I find something like
this:(just copy and paste)
-----------------------------------------
(setq gnus-newsrc-alist '(("nnfolder+archive:sent-08.2004" 3 ((1 . 1))
nil (nnfolder "archive" (nnfolder-directory "~/Mail/archive")
(nnfolder-active-file "~/Mail/archive/active") (nnfolder-get-new-mail
nil) (nnfolder-inhibit-expiry t)))
-----------------------------------------
There are something like (nnfolder-directory %^^&&*). WHY!? I have
never used `nnfolder' _and_ I have searched my `.gnus.el', there is no
word `nnfolder'! I use nnml as my mail backend and archive method and I
have deleted the old newsrc.old. That is impossible.

I am confused, really.
My gnus version is 5.10.6 .
Is it a bug? I don't think I have done anything wrong or where can i
find help?

Thanks!