Extending 'emacs-lisp-mode' Disables 'auto-complete' for It

[Haroogan]

Hello,

I've extended emacs-lisp-mode with my elisp-mode in order to provide 
more syntax highlighting. Relevant excerpt:

...

(define-derived-mode elisp-mode
  emacs-lisp-mode
  "?L"
  "A major mode for Emacs Lisp.
\\{elisp-mode-keymap}"
  (set 'font-lock-defaults '((elisp-mode-font-lock-keywords)))
  (set-syntax-table elisp-mode-syntax-table)
  (use-local-map elisp-mode-keymap)
  (run-hooks 'emacs-lisp-mode-hook); Tried `run-mode-hooks` as well...
  (run-mode-hooks 'elisp-mode-hook))

(provide 'elisp)

Then I have:

(add-hook 'emacs-lisp-mode-hook 'ac-emacs-lisp-mode-setup)

And of course:

(require 'elisp)

(add-to-list
 'auto-mode-alist
 '("\\.el" . elisp-mode))

Now the problem is that auto-completion doesn't work in elisp-mode.
I have no clue why.
As soon as I disable elisp-mode and return to the emacs-lisp-mode it 
works just fine.
I've also tried:

(add-hook 'elisp-mode-hook 'ac-emacs-lisp-mode-setup)

and without luck...

Any help is appreciated.
Thanks.