>>>>> In <yotlllgaofhv.fsf@jpl.org> 
>>>>>    Katsumi Yamaoka <yamaoka@jpl.org> wrote:

> Do you use `setq' to modify hook variables?  Some T-gnus hook
> variables have significant values by default and `setq' will
> break them.  Although it may not be by you, `setq' is apt to be
> used in very old .emacs file.

> See the value for the message-setup-hook variable using `C-h v'.
> If it doesn't contain `turn-on-mime-edit', you surely have a
> problem as mentioned above.  Otherwise, you will need to show us
> your .emacs file, and also .gnus.el file if it exists.

And to modify some T-gnus hook variables in .emacs file also
will break those default values even if you use `add-hook'
rather than `setq'.  Using ~/.gnus.el file to customize Gnus is
strongly recommended.