The section 'Displaying in the Margins
<https://www.gnu.org/software/emacs/manual/html_node/elisp/Display-Margins.html>'
of the elisp manual mentions
that 'To display something in the margin in association with certain
buffer text ... put a before-string property on the text and put the
margin display specification on the contents of the before-string'.

So this is what I am trying to achieve using the following code

```
(defun baleen-render (data)
  (pop-to-buffer (get-buffer-create "*baleen*"))
  (set-window-margins nil 5)
  (dolist (page data)
    (dolist (match (cdr page))
      (let ((o (make-overlay (point)
                             (progn (insert match)
                                    (point)))))
        (let ((s " "))
          (put-text-property 0 1
                             'display `((margin left-margin) ,(format " %d"
(car page)))
                             s)
          (overlay-put o 'before-string s)))
      (insert "\n"))))

(baleen-render '((1 "test1" "test2") (2 "test3")))
```

Here, for every 'match' in a 'page' I am creating a new string 's'
to which I add the margin display property to 'associate' it
with some buffer text by using it as the value for its before-string
property.
However, although each 's' should get a different display property value
via (format " %d" (car page)), all margin entries end up showing the
same value of 2 (while the first two lines should show page number 1).

To reproduce the error, simply evaluate the code above. Using edebug on
'baleen-render' it can be seen that the code seems correct, i.e. (car
page) correctly returns the correct page number.

It seems that although I am creating a different string object on each
iteration, somehow the object put in the marging seems to be always the
same.

To me, this looks like a bug. And otherwise, if I am doing something
wrong, then of course this report can be seen as a 'help/support
request'. Thanks!

In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.34, cairo version 1.17.6) of 2022-09-10 built on fedora
Repository revision: 4cf9c92e27d20da9453f9abe89d84bee5d776329
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12014000
System Description: Fedora Linux 37 (Workstation Edition)

Configured using:
 'configure --with-modules --with-cairo --with-native-compilation
 --with-json'

Configured features:
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XINPUT2 XPM GTK3 ZLIB

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Load-path shadows:
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Features:
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Memory information:
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