This was observed on this very instance. My email notification settings for Maniphest are:
However I've observed a few times that I've received notification emails for "changed subscribers" like this one a few hours ago:
From: epriestley (Evan Priestley) <noreply@phabricator.com> Date: Fri, Apr 15, 2016 at 5:14 AM Subject: [Maniphest] [Changed Subscribers] T4103: Implement "Role Profiles" to provide search, homepage and application defaults To: <REDACTED> epriestley added a subscriber: nicorac. epriestley merged a task: T10821: Add default settings for newly created accounts. TASK DETAIL https://secure.phabricator.com/T4103 EMAIL PREFERENCES https://secure.phabricator.com/settings/panel/emailpreferences/ To: epriestley Cc: nicorac, isfs, ofbeaton, jasonfsmitty, revi, r0bbie, dans, richardvanvelzen, ProfFan, JOY, ablekh, carwyn, jithinvmohan, featherless, arune, edibiase, kymera.travis, gou1, gerx03, cspeckmim, srijan, jayvdb, nickz, aHa, eadler, maiki, joshuaspence, mirrom, Mnkras, djc, metellius, trsystran, MZMcBride, devurandom, johnny-bit, scfc, timor, jbrown, aklapper, bigo, mikerbrewster, m.capobianco, chad, lpriestley, ite-klass, noisy, shadowhand, avivey, wotte, cburroughs, chasemp, philippe.jadin, swisspol, btrahan, hsnim, michaeloa, asherkin, epriestley, vandana9, allan.laal, hach-que