Why is minor mode map not overriding major mode?

Question

If I have both a major and minor mode in effect, I expect that the MINOR keymap will override. But that's not what happens!

The major map has (among other things) a weird binding for SPC, and it does not have any inserts. By contrast, the minor map inherits from text-mode.

But when the minor mode is in effect, I still don't get any self-inserts, and SPC is still weird. I do see my additional custom minor mode commands. But I wanted the inherited text-mode keys to override the ones that the major mode redefined.

Do I misunderstand the precedence of how keys are looked up, or have I somehow defined my keymaps incorrectly, or is the problem in my mode definitions?

Here is the simplified code:

;; MAJOR MODE

(defvar-keymap sd-mode-map
  :parent nil  ;still gets most commands?
  :suppress t  ;get rid of self-insert
  "SPC"     'sd-next-line)

(defun sd-mode ()
  [...]  
  (interactive)
  (delay-mode-hooks
    (setq major-mode 'sd-mode)  
    (kill-all-local-variables)
    (use-local-map sd-mode-map)
    ;; business
    (setq buffer-read-only t))
  (run-mode-hooks 'sd-mode-hook))

;; MINOR MODE

(defvar sd-edit-mode-map
  (let ((map (make-sparse-keymap "Sd/Edit")))
    (set-keymap-parent map text-mode-map)
    (define-key map "<right>" 'sd-some-thing)
    map)
  "My minor mode keymap")

(define-minor-mode sd-edit-mode
  "Whatever."
  :keymap sd-edit-mode-map
  (message "Your minor mode is in effect!")
  (setq buffer-read-only nil))

Answer 1

The self-insert-command bindings do not come from text-mode map; they come from the global map. The other problem is that the :suppress feature on the major mode keymap will still prevent the minor keymap from seeing the normal self-insert-commands (even when the minor mode's keymap inherits from global-map).

Just make sure that the major mode puts the buffer in read-only mode, don't suppress the self-insert commands.