Run test1 in the code snippet below for reproducing the bug.

I tested it using emacs -Q on macOS and Ubuntu with the same result.


(setq *MULTI-LAB-ENTRY-RE* "^\\([[:alpha:]]\\)?[[:space:]]?\\([[:digit:]]\\{2\\}/[[:digit:]]\\{2\\}/[[:digit:]]\\{4\\}\\)[[:space:]]+\\([[:digit:]]\\{2\\}:[[:digit:]]\\{2\\}\\)[[:space:]]+\\(.+\\)")


(defun test1 ()
  (let ((line "a 05/22/2025 14:32 BLOOD WBC 10.4 H K/uL 4.5 - 10.0"))
    (string-match *MULTI-LAB-ENTRY-RE* line)
    (message "match-data after string-match: %S" (match-data))
    (split-string "dummy string") ;; Do NOT pass 'line' here
    (message "match-data after split-string: %S" (match-data))
    (message "group 1: %S" (match-string 1))))

(test1)




In GNU Emacs 30.1 (build 1, aarch64-apple-darwin21.6.0, NS
appkit-2113.65 Version 12.7.6 (Build 21H1320)) of 2025-02-24 built on
armbob.lan
Windowing system distributor 'Apple', version 10.3.2575
System Description:  macOS 15.5

Configured using:
'configure --with-ns '--enable-locallisppath=/Library/Application
Support/Emacs/${version}/site-lisp:/Library/Application
Support/Emacs/site-lisp' --with-modules 'CFLAGS=-DFD_SETSIZE=10000
-DDARWIN_UNLIMITED_SELECT' --with-x-toolkit=no'

Configured features:
ACL GLIB GMP GNUTLS JPEG LIBXML2 MODULES NOTIFY KQUEUE NS PDUMPER PNG
RSVG SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER WEBP XIM ZLIB

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

Major mode: ELisp/d

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  minibuffer-regexp-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 message 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 subr-x mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
help-fns radix-tree cl-print byte-opt gv bytecomp byte-compile debug
backtrace help-mode find-func misearch multi-isearch cl-loaddefs cl-lib
rmc iso-transl tooltip cconv eldoc paren electric uniquify ediff-hook
vc-hooks lisp-float-type elisp-mode mwheel term/ns-win ns-win
ucs-normalize mule-util term/common-win 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 kqueue cocoa ns multi-tty
make-network-process emacs)

Memory information:
((conses 16 53177 15615) (symbols 48 6410 0) (strings 32 16110 2304)
(string-bytes 1 411336) (vectors 16 11797)
(vector-slots 8 134092 12148) (floats 8 25 52) (intervals 56 375 7)
(buffers 992 12))