OwnCloud 10.0.8 - Strange issue with reminders to an event appearing out of nowhere on iOS/iPhone


I got a strange issue and I need help to find a work-a-round or the actual reason (so it can be fixed):

I’m synching my business appointments from outlook to an ownCloud server using CalDav Synchronizer.
In CalDAV Synchronizer I’m supressing reminders as I do not want my private mobile to actively remind me.
I’m synching my iPhone with OwnCloud using the build in functionality.

tldr: outlook->caldav synchronizer(map reminders: no)->caldav(ownCloud)->iPhone

When I look at the appontments using the WebGui/Calendar App of my onwCloud server there are NO reminders. When I look at my iPhone - there is (out of nowhere) a reminder one hour before the event.

Other discoveries:
This does ALSO happen when I create an appoinment directly using the OwnCloud Calender App.
This does NOT happen when I create an appontment on my iPhone.

It just happens when I synchronize an appointment from business outlook to caldav and then to iOS.
So it probably Caldav Synchronizer is involved too…

Any help highly appreciated…

UPDATE: I found that disabling the default reminder in the iOS/calender settings of my iPhone is a work around. However this is not a good solution because then I need to manually create a reminder every time I ACTUALLY create a new entry myself. I would like to find a way to just prevent the iPhone to create an entry for events created somewhere else and then getting synchronized to it…

Update2: I had another intersting find:
a) I created an event on iOS with default reminders disabled. Synched to caldav - deleted calendar on iphone - enabled default reminder - synched -> default reminder was created
b) I created an event on iOS with default reminder on - REMOVED the reminder on iOS -> synched to caldav - deleted calendar on iPhone -> synched again -> no reminder created
So somehow iOS seems to be able to detect if the default reminder was removed at a point in time also I deleted the whole calendar on the phone first…

I think however that ownCloud is not the right or only place to fix that…it’s either up to apple or probably caldav synchronizer as a work-a-round.