Hello. You application is good, but you really need to do something with time zones handling. Looks like that you store local times for the events and updating them, when time zone is changed in preferences. If so this is very ugly and this is not the way it should be done. The problem I was having is that I have changed time zone from Moscow to Prague and that leads to insane results. It started to change all my schedules in Google Calendar and I even was not able to change it back - it have changed it again and again. I haven't time to debug what exact behaviour of this bug, because I was more interested in not ruining my whole schedule. So I just turned off sync with calendar.