PS. I've reproduced the problem with commit a14821d615; you can ignore
the "Repository revision" and "Repository branch" fields below.

In GNU Emacs 29.0.60 (build 4, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.16.0, Xaw scroll bars) of 2022-12-29 built on alto
Repository revision: f26689637923ac9b834a209e1bab09c779be212f
Repository branch: emacs-29-mdk
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Debian GNU/Linux 11 (bullseye)

Configured using:
 'configure --prefix=/usr/new'

Configured features:
CAIRO FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG LIBSELINUX
LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG SECCOMP SOUND THREADS TIFF
TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM LUCID ZLIB

Important settings:
  value of $LC_TIME: C
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: MH-Folder

Minor modes in effect:
  hl-line-mode: t
  shell-dirtrack-mode: t
  delete-selection-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  buffer-read-only: t
  column-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow mh-identity mh-letter emacsbug sort gnus-async gnus-bcklg
gnus-kill qp cl-extra help-mode gnus-ml disp-table url-http url-gw
url-cache url-auth url-handlers nnrss mm-url nndoc nndraft
network-stream nsm gnus-agent gnus-srvr nnvirtual nntp gnus-cache
textsec uni-scripts idna-mapping ucs-normalize uni-confusable
textsec-check mm-archive mail-extr mh-mime mule-util mh-thread mh-show
goto-addr gnus-cite mh-inc hl-line mh-tool-bar mh-acros mh-seq mh-xface
mh-utils mh-folder which-func imenu misearch multi-isearch crm thingatpt
cus-edit pp cus-start cus-load mdk-mail gnus-mh gnus-msg mh-comp mh-scan
mh-gnus gnus-dup nnmh gnus-score score-mode gnus-art mm-uu mml2015
mm-view mml-smime smime gnutls dig gnus-sum shr pixel-fill kinsoku
url-file svg dom browse-url url url-proxy url-privacy url-expand
url-methods url-history url-cookie generate-lisp-file url-domsuf
url-util url-parse auth-source cl-seq eieio eieio-core cl-macs json map
gv url-vars gnus-group gnus-undo gnus-start gnus-dbus dbus xml
gnus-cloud nnimap nnmail mail-source utf7 nnoo parse-time iso8601
gnus-spec gnus-int gnus-range gnus-win gnus nnheader range wid-edit mh-e
mh-buffers mh-loaddefs message sendmail mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date mm-decode mm-bodies
mm-encode mail-parse rfc2231 rfc2047 rfc2045 mm-util ietf-drums
mail-prsvr mailabbrev mail-utils gmm-utils mailheader warnings server
noutline outline icons cc-mode cc-fonts cc-guess cc-menus cc-cmds
cc-styles cc-align cc-engine cc-vars cc-defs byte-opt bytecomp
byte-compile shell subr-x pcomplete comint ansi-osc ansi-color ring
xcscope advice delsel vc vc-dispatcher timeclock cl-loaddefs cl-lib
mdk-hacks rmc iso-transl tooltip cconv eldoc paren electric uniquify
ediff-hook vc-hooks lisp-float-type elisp-mode mwheel term/x-win x-win
term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode lisp-mode prog-mode register
page tab-bar menu-bar rfn-eshadow isearch easymenu timer select
scroll-bar mouse jit-lock font-lock syntax font-core term/tty-colors
frame minibuffer nadvice seq simple cl-generic indonesian philippine
cham georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese composite emoji-zwj charscript
charprop case-table epa-hook jka-cmpr-hook help abbrev obarray oclosure
cl-preloaded button loaddefs theme-loaddefs faces cus-face macroexp
files window text-properties overlay sha1 md5 base64 format env
code-pages mule custom widget keymap hashtable-print-readable backquote
threads inotify dynamic-setting system-font-setting font-render-setting
cairo x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 350237 71147)
 (symbols 48 23107 9)
 (strings 32 88955 27698)
 (string-bytes 1 2387295)
 (vectors 16 66600)
 (vector-slots 8 1547532 240746)
 (floats 8 253 414)
 (intervals 56 767 0)
 (buffers 976 22))