program dies with 'Wide character in subroutine entry at /usr/bin/listadmin line 556'

Imported from Debian bug http://bugs.debian.org/886247:

Package: listadmin
Version: 2.42-1
Severity: normal

If I press 'b' to check the body of the mail, the program dies.
This is the first time in a lot of years of moderation, so I assume bad formatting in spam.

[2/4] ============== <email address hidden> =========================
From: <spammer address removed>
Subject: Re: notification #4393 for <email address hidden>
Reason: Post by non-member to a members-only list Spam? 0
Approve/Reject/Discard/Skip/view Body/Full/jump #/Undo/Help/Quit ? b
Wide character in subroutine entry at /usr/bin/listadmin line 556.

-- System Information:
Debian Release: 9.3
  APT prefers stable
  APT policy: (1000, 'stable'), (995, 'stable'), (500, 'stable-updates')
Architecture: amd64 (x86_64)

Kernel: Linux 4.13.0-0.bpo.1-amd64 (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages listadmin depends on:
ii libcrypt-ssleay-perl 0.73.04-2
ii libnet-inet6glue-perl 0.603-2
ii libtext-reform-perl 1.20-3
ii libwww-perl 6.15-1

listadmin recommends no packages.

listadmin suggests no packages.

-- no debconf information