call from xdg-email with attachment crashes claws-mail

When claws-mail is set s the default email client, calling
xdg-email --subject HELLO --body "Body text" --attach FILENAME EMAILADDRESS
causes claws-mail to terminate.
No errors are reported to the terminal

Any call without "--attach FILE" works fine.

This bug also affects LibreOffice "send", where it appears that the problem may be related to an encoded filename.

It also affects simplescan "send" function, already reported as Bug #1909941,
where it is suggested that the problem may have gone away in Claws version 3.17.8
But this is not available in Ubuntu 20.04 LTS, and in the meantime simplescan and LO have missing functionality.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: claws-mail 3.17.5-2
ProcVersionSignature: Ubuntu 5.4.0-73.82-generic 5.4.106
Uname: Linux 5.4.0-73-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.17
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: X-Cinnamon
Date: Thu May 13 11:33:19 2021
InstallationDate: Installed on 2017-03-09 (1525 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
SourcePackage: claws-mail
UpgradeStatus: Upgraded to focal on 2020-09-30 (224 days ago)