I've reported the following bug upstream:

With GNU Screen v5, the U+200B ZERO WIDTH SPACE character
(UTF-8: E2 80 8B) can corrupt the screen display, as seen with Mutt.

Consider a mbox file containing twice the following message:

  From a@b.invalid Fri Apr 24 08:48:52 2026
  From: a@b.invalid
  Subject: =?utf-8?Q?=E2=80=8B.abcdefghijklmnopqrstuvwxyz.1234567890?=
  Date: Fri, 24 Apr 2026 08:48:27 +0200

(file "mbox" attached) and two possible muttc files:

* muttrc-1 with just the following line:

set arrow_cursor

* muttrc-2 with the following two lines:

set arrow_cursor
color index lightcyan black .

For the screenrc file, it is better to have "defbce on" for
GNU Screen v4 (wih my tests, it ensures a consistent background,
but it does not have any effect on how the text is positioned).

In a 80-column xterm, without GNU Screen or with GNU Screen v4
(package screen 4.9.1-3.1), the following commands

    mutt -n -F muttrc-1 -f mbox
    mutt -n -F muttrc-2 -f mbox

both give a correct output:

q:Quit  d:Del  u:Undel  s:Save  m:Mail  r:Reply  g:Group  ?:Help
->    1 N   Apr 24 a@b.invalid     (  0K) .abcdefghijklmnopqrstuvwxyz.1234567890
      2 N   Apr 24 a@b.invalid     (  0K) .abcdefghijklmnopqrstuvwxyz.1234567890
---Mutt: mbox [Msgs:2 New:2 0.3K]---(date/date)-------------------------(all)---

(screenshot attached: xterm-screen-4.png).

Now, with GNU Screen v5 (package screen 5.0.1-1.1) in a 80-column xterm:

* with "mutt -n -F muttrc-1 -f mbox":

q:Quit  d:Del  u:Undel  s:Save  m:Mail  r:Reply  g:Group  ?:Help
->    1 N   Apr 24 a@b.invalid     (  0K) .abcdefghijklmnopqrstuvwxyz.1234567892
 N   Apr 24 a@b.invalid     (  0K) .abcdefghijklmnopqrstuvwxyz.1234567890