Try one or all of this:

    (require 'dired+)                                                              
    (setq diredp-bind-problematic-terminal-keys nil)
                       
    (defun dired-custom()                                                          
      "conf dired-mode"
      (diredp-toggle-find-file-reuse-dir t)                                           
      (local-set-key (kbd "M-O") nil))                                             
    (add-hook 'dired-mode-hook 'dired-custom)
         
    (eval-after-load 'dired-mode '(define-key dired-mode-map (kbd "M-O") nil))