User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Firefox/45.0 Build ID: 20160502160818 Steps to reproduce: UserA and UserBoss are 2 users on the same Caldav server (reproduced with Oracle Convergence Communication). UserA has read and write permission on userBoss calendar. 1. UserA subscribes only to his calendar 2. UserA subscribes to userBoss calendar, no email associated to this calendar 3. UserA creates an event in userBoss calendar and opens the attendees dialog to add some attendees 4. UserA restarts Thunderbird 5. UserA creates an event in userBoss calendar and opens the attendees dialog to add some attendees Actual results: * Step 3: the organizer is userA, as wanted by Lightning (based on https://bugzilla.mozilla.org/show_bug.cgi?id=1217505#c1). In the attendee dialog, the first line is firstname.lastname@example.org, which is OK * Step 5 The organizer is now userBoss In the attendee dialog, the first line is email@example.com, which is the email of userBoss The reproduction is possible up to... 80% I guess. Sometimes the organizer is directly userBoss at step 3. Expected results: In step 3 and step 5, the organizer should be userA. When this bug occurs and userBoss becomes the organizer, the bug https://bugzilla.mozilla.org/show_bug.cgi?id=1273431 is not reproduced anymore.