Users that have set their email preferences to ignore changes of subscribers in tasks, still will receive notifications when someone subscribes / unsubscribes via email (not via web). The reason is that such actions are interpreted incorrectly as comments as well.
Example of a wrong email notification received:
```
Subject: [Maniphest] [Commented On] T65971: iOS app doesn't support {{DISPLAYTITLE:}}
Deskana removed a subscriber: Deskana.
Deskana added a comment.
...
```
If you look at https://phabricator.wikimedia.org/T65971#1328988, he didn't leave a comment.
Original report: https://phabricator.wikimedia.org/T101106