I encountered a bug when replacing regular expressions. If you [u]ndo a previous change during the replacement process, subsequent changes to the \2 substitution will use the old undone result. Text: --- Aaaaa. Bbbb. Ccccc. Dddd. Eeeee. Ffff. Ggggg. Hhhh. --- Input regexp: \([.]\) \([A-Z]\) Output regexp: \1 \2 Bug: 1. Copy the text above to the buffer. 2. Enter the regular expressions to the interactive regexp replacement [ C-M-%]. 3. Click [y] twice until the Ffff is highlighted. 4. Cancel the previous replacement via [u]. 5. Continue replacing [y] until the end. 6. Notice that all sentences except the first and second now begin with an incorrect letter D, which is not implied by the entered regexp, it should be F and H, as if it had been replaced, but without being undoed in the middle of the process. Output: --- Aaaaa. Bbbb. Ccccc. Dddd. Eeeee. Dfff. Ggggg. Dhhh. --- In GNU Emacs 29.3 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.38, cairo version 1.16.0) of 2024-05-20, modified by Debian built on sbuild Windowing system distributor 'The X.Org Foundation', version 11.0.12101007 System Description: Debian GNU/Linux 12 (bookworm) Configured using: 'configure --build x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib --libexecdir=/usr/libexec --localstatedir=/var/lib --infodir=/usr/share/info --mandir=/usr/share/man --with-libsystemd --with-pop=yes --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/29.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/29.3/site-lisp:/usr/share/emacs/site-lisp --with-sound=alsa --without-gconf --with-mailutils --with-native-compilation --build x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib --libexecdir=/usr/libexec --localstatedir=/var/lib --infodir=/usr/share/info --mandir=/usr/share/man --with-libsystemd --with-pop=yes --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/29.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/29.3/site-lisp:/usr/share/emacs/site-lisp --with-sound=alsa --without-gconf --with-mailutils --with-native-compilation --with-cairo --with-x=yes --with-x-toolkit=gtk3 --with-toolkit-scroll-bars 'CFLAGS=-g -O2 -ffile-prefix-map=/build/reproducible-path/emacs-29.3+1=. -fstack-protector-strong -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro' Configured features: ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NATIVE_COMP NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB Important settings: value of $LC_MONETARY: ru_RU.UTF-8 value of $LC_NUMERIC: ru_RU.UTF-8 value of $LC_TIME: ru_RU.UTF-8 value of $LANG: ru_RU.UTF-8 value of $XMODIFIERS: @im=ibus locale-coding-system: utf-8-unix Major mode: Fundamental Minor modes in effect: save-place-mode: t global-tab-line-mode: t tab-line-mode: t global-display-line-numbers-mode: t display-line-numbers-mode: t electric-pair-mode: t desktop-save-mode: t delete-selection-mode: t tooltip-mode: t global-eldoc-mode: t show-paren-mode: t electric-indent-mode: t mouse-wheel-mode: t menu-bar-mode: t file-name-shadow-mode: t global-font-lock-mode: t font-lock-mode: t blink-cursor-mode: t column-number-mode: t line-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 sort mail-extr emacsbug misearch multi-isearch mm-archive message sendmail dired dired-loaddefs rfc822 mml mml-sec epa derived gnus-util text-property-search mailabbrev gmm-utils mailheader mm-decode mm-bodies mm-encode mail-utils mule-util gnutls network-stream url-cache url-http url-auth mail-parse rfc2231 rfc2047 rfc2045 mm-util ietf-drums mail-prsvr url-gw nsm puny epg rfc6068 epg-config comp comp-cstr warnings cus-edit pp cus-start wid-edit cl-extra help-mode yank-media markdown-mode thingatpt noutline outline icons time-date vc-git diff-mode easy-mmode vc-dispatcher python rx project pcase treesit comint ansi-osc ring ansi-color gruvbox-dark-hard-theme gruvbox autothemer color lisp-mnt dash saveplace whitespace tab-line display-line-numbers elec-pair desktop frameset delsel cus-load finder-inf csv-mode-autoloads info markdown-mode-autoloads po-mode-autoloads tree-sitter-autoloads tsc-autoloads package browse-url url url-proxy url-privacy url-expand url-methods url-history url-cookie generate-lisp-file url-domsuf url-util mailcap url-handlers url-parse auth-source cl-seq eieio eieio-core cl-macs password-cache json subr-x map byte-opt gv bytecomp byte-compile url-vars cl-loaddefs cl-lib cyril-util 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 dbusbind inotify lcms2 dynamic-setting system-font-setting font-render-setting cairo move-toolbar gtk x-toolkit xinput2 x multi-tty make-network-process native-compile emacs) Memory information: ((conses 16 422703 549886) (symbols 48 21740 133) (strings 32 123122 109316) (string-bytes 1 5309779) (vectors 16 36085) (vector-slots 8 683635 189466) (floats 8 249 448) (intervals 56 999 1339) (buffers 984 19))