Comment 43 for bug 1748895

And further to my last comment, the point is proved.
Claws[-mail] is set in senddoc to use
ATTACH="${ATTACH:-}${ATTACH:+ }$2"
without any reference to encoding.

In Tools.Options, I set email to /usr/bin/claws-mail
and all is well, the document is attached to a draft email in a Compose window.

The use of URI_ENCODE in conjunction with the attachment filename seems to be wrong - though why it caused no problems until recently I do not understand!