Maybe you can try to fix your issue by forcing the buffer-undo-list variable to nil for the elisp mode, as follow: (add-hook 'elisp-mode (lambda () (setq-local buffer-undo-list nil)))

I tried it but still no joy...

Looking at this issue I noticed 3 things that may help to pinpoint the origin...:

• I have 2 variables set that affect the scratch buffer in my config (without yours, that it's the 3rd):

                  (setq initial-major-mode 'org-mode)
                  (setq-default major-mode 'org-mode)

• Before this reply, (setq-default major-mode 'org-mode) was (setq default-major-mode 'org-mode). Both expressions seems indistinguishable in the resulted behavior.
• The scratch buffer starts in org-roam mode (and read-only mode), which is very strange, but can obviously be related and/or part of the problem. The org-roam section (my config is literate in org-mode) comes before this variables being set.

What does this info may imply?

Hello Sunoc.

• the buffer is not in read-only, but it always start as so.
• the keybinding is ok since it works in all the rest of the buffers.
• Upon calling undo, emacs says "no undo information in this buffer" (searching for this didn't seem to give relevant information except something from 2006 and then something about specific of a table-spreadsheet that I don't use).

From this and @[email protected] (I will relpy after this one) it looks that it may be my configuration, since I'm using vanilla emacs with my own configuration.

Anyway, thanks a lot for your time! :)