dired-mode uses hard-coding when it rebinds some global key bindings.
For example, there is the following line in dired.el file:

    (define-key map "\C-n" 'dired-next-line)

Therefore it overrides the global C-n key, whatever its command is in
user's keymap. The command should be bound like this:

    (define-key map [remap next-line] 'dired-next-line)

Using [remap ...] is preferred because it makes it possible for user to
redefine the global keymap they way she wishes and keys will still
automatically get their mode-specific behaviour. The attached patch
fixes this for dired-mode.