bug#39149: 27.0.50; describe-buffer-bindings is calling :filter function in wrong buffer

[Stefan Kangas <stefankangas@gmail.com>]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> yyoncho <yyoncho@gmail.com> writes:
>
>> To reproduce (eval in scratch buffer)
>> (define-key global-map (kbd "C-c C-l r")
>>   `(menu-item "2" switch-to-buffer
>>               :filter ,(lambda (cmd)
>>                          (print (format "Called in %s" (current-buffer)))
>>                          cmd)))
>> (with-temp-buffer
>>   (with-output-to-string
>>     (describe-buffer-bindings (get-buffer "*scratch*") [3 12] t)))
>>
>> This outputs:
>>
>> \"Called in  *temp*\"
>
> I tried this recipe, but I'm not getting the :filter function called at
> all.  Do you have a recipe, starting from "emacs -Q", that reproduces
> this bug?
>
> And your report didn't include the data about the version generated by
> report-emacs-bug, so it's hard to guess whether bug is only on some
> specific system.

I can reproduce the above on Emacs 26.3, but not on master.

Note that there might have been changes here with the merge of
scratch/substitute-command-keys.  I tried hard to not introduce any
regressions or even changes in behavior with that branch, but I might
have failed to include the above bug...

What is the result output here?  Here, the last form evaluates to this
on master:

"\f
Global Bindings Starting With C-c C-l:
key             binding
---             -------

\f
Function key map translations Starting With C-c C-l:
key             binding
---             -------

"

Is this correct?  Should it do anything else in addition that it
currently does not?