bug#38992: 27.0.60; when enabled, fido-mode seems to break vc-git-grep

[waah]

--text follows this line--

start emacs via 'emacs -Q', enable fido-mode (via M-x), open file in git 
repository and run command
vc-git-grep (again via M-x)

error message is:

Error in post-command-hook (icomplete-post-command-hook):
(wrong-type-argument stringp ("*.F90" "all" "el" "ch" "c" "cc" "cchh"
"hh" "h" "l" "m" "tex" "texi" "asm"))

without fido-mode everything works as expected.

In GNU Emacs 27.0.60 (build 1, x86_64-pc-linux-gnu, GTK+ Version 2.24.31)
 of 2020-01-06 built on cloten
Repository revision: 088bfcc2d80eed44864147f3491eff69e4eb5cd8
Repository branch: HEAD
Windowing system distributor 'The X.Org Foundation', version 11.0.11803000
System Description: openSUSE Leap 42.3

Recent messages:
You can run the command ‘vc-git-grep’ with M-x v-gr RET
Grep finished with 7 matches found
Fido mode enabled
Error in post-command-hook (icomplete-post-command-hook): (wrong-type-argument 
stringp ("*.F90" "all" "el" "ch" "c" "cc" "cchh" "hh" "h" "l" "m" "tex" "texi" 
"asm"))
backward-delete-char: Text is read-only
Grep finished with no matches found
Quit

Configured using:
 'configure --with-gif=ifavailable CC=gcc'

Configured features:
XPM JPEG TIFF PNG SOUND DBUS GSETTINGS GLIB NOTIFY INOTIFY GNUTLS
LIBXML2 FREETYPE HARFBUZZ XFT ZLIB TOOLKIT_SCROLL_BARS GTK2 X11 XDBE XIM
MODULES THREADS PDUMPER LCMS2

Important settings:
  value of $LC_COLLATE: POSIX
  value of $LC_CTYPE: en_GB.UTF-8
  value of $LANG: en_GB.utf8
  value of $XMODIFIERS: @im=local
  locale-coding-system: utf-8-unix

Major mode: Messages

Minor modes in effect:
  icomplete-mode: t
  tooltip-mode: t
  global-eldoc-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
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny format-spec rfc822 mml
mml-sec epa derived epg epg-config gnus-util rmail rmail-loaddefs
text-property-search time-date mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils mule-util tango-dark-theme
eieio-opt cl-extra speedbar sb-image ezimage dframe find-func
vc-annotate vc-dir ewoc vc vc-dispatcher vc-filewise help-fns radix-tree
help-mode ffap url-parse auth-source cl-seq eieio eieio-core cl-macs
eieio-loaddefs password-cache json subr-x map seq byte-opt gv bytecomp
byte-compile cconv url-vars thingatpt grep compile comint ansi-color
ring vc-git diff-mode easy-mmode f90 cus-edit easymenu wid-edit
cl-loaddefs cl-lib misearch multi-isearch cus-start cus-load icomplete
dired dired-loaddefs tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type 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 elisp-mode lisp-mode prog-mode register page tab-bar menu-bar
rfn-eshadow isearch timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors frame minibuffer cl-generic
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 charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote threads dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 106359 11893)
 (symbols 48 11215 1)
 (strings 32 33745 1223)
 (string-bytes 1 1021750)
 (vectors 16 16353)
 (vector-slots 8 197937 15512)
 (floats 8 63 313)
 (intervals 56 869 95)
 (buffers 1000 18)
 (heap 1024 16363 1478))