At least the underlying cause is known. I will post a report
to freedesktop.org as you suggest.
Still don't understand why uninstalling the "Nimbus Sans"
font family causes Inkscape to substitute "Sans" in place of
"Helvetica" when I select "Helvetica".
When I can, I will try to reinstall "Nimbus Sans" and see
what Inkscape does.
At least the underlying cause is known. I will post a report
to freedesktop.org as you suggest.
Still don't understand why uninstalling the "Nimbus Sans"
font family causes Inkscape to substitute "Sans" in place of
"Helvetica" when I select "Helvetica".
When I can, I will try to reinstall "Nimbus Sans" and see
what Inkscape does.