Re: Default :group in lisp/emacs-lisp/easy-mmode.el.

[Richard Stallman]

    After Lute's patch the define-minor-mode for `diff-minor-mode' would
    have to be given an explicit :group, or diff-minor-mode-hook would be
    moved from the diff-mode group (where it belongs) to the bogus
    diff-minor group (if I understood Lute's patch correctly).  I am now
    convinced that there must be tons of other examples.

There seem to be 85 calls to define-minor-mode in the Emacs sources.
I guess the first order of business would be to make sure each of them
has an explicit :group.