Thanks a bunch for solving this so quickly :)

Applied the patch but it doesn't seem to solve the issue unfortunately. Still looks the same as before, author not added to subscribers

Looks exactly like what we're getting on our setup. You shouldn't get a mail now since you're not on any To/Cc-list

No change unfortunately, this is what it looks like:

I used the .bin/mail script to see outgoing, and no mail is sent to the author-user unless manually added to subscribers

People send emails to our bug-email, fetchmail fetches it, passes on to procmail which sends it to mail_handler.php. Ticket gets created, sender gets added to author (if the address is unknown, we're setting a "catch-all" account as author), but does not get added to subscribers, and therefore won't get any updates when we change things in the ticket unless we manually add the person to subscribers. I will upgrade to the latest version just to be sure, but I can't see any changes related to our issue.

They do, but most people adding issues are non-IT personel, and their tech-proficiency varies widely, so we've chosen to recommend email for posting issues.