0) Register, confirm email, subscribe to some tasks and whatever
1) Visit https://phabricator.wikimedia.org/settings/panel/emailpreferences/
2) Set some dropdown in "Maniphest Tasks" to "Ignore" (I did "A task's subscribers change." and " A task's associated projects change.")
3) [Wait.] Visit https://phabricator.wikimedia.org/notification/
I. Expected: no notifications of the ignored kind are shown, i.e. I receive less notifications than the two "higher" levels in the dropdown, "Email" and "Notification". (Expectation confirmed upstream: https://secure.phabricator.com/differential/changeset/?ref=167553&whitespace=ignore-all )
II. Observed: I have several, e.g. https://phabricator.wikimedia.org/T74740#786993 https://phabricator.wikimedia.org/T857#786815 ; those tasks are not in projects I watch, I'm not more than a subscriber to those tasks and I don't have Herald rules enabled (because Herald is disabled for me).
Hoo confirmed he sees several "updated subscribers of" in https://phabricator.wikimedia.org/notification/query/all/ after setting the event to "ignore".
Krenair and Nemo were NOT able to reproduce the bug upstream, https://secure.phabricator.com/T5908#86041 Qgil's hypothesis is that the bug is caused by T765.