trouble adding keyboard shortcut to ibuffer mode

[Christian Seberino]

The following does NOT reset C-o (Control key + o) in ibuffer mode.
Why not?

 (add-hook 'ibuffer-mode-hook '(lambda ()
                                      (global-set-key (kbd "C-o")
'find-file)
                                      (ibuffer-auto-mode t)

(ibuffer-switch-to-saved-filter-groups "")
                                      ))