Fourth, is
this distro-specific? My system has neither update-mime nor /usr/lib/mime,
suggesting that this utility is not universal.
Yes, this is Debian-specific.
Slackware has update-mime-database, which is why I asked for other apps besides Chromium
to test the problem. If this is distro-specific perhaps we at least could share how to
replicate and also resolve the problem, and which distros are/might be involved.
Darrell