Please see https://forums.bitfire.at/post/12828
CalDAV Sync doesn't handle recurring event modifications correctly with Horde
I’m using Horde as my CalDAV server, and I’ve done things such as the following:
Have a long-time recurring event, such as daily work schedule that repeats every M-F at the same times. For holidays and days off, I would delete those days for that specific event in the calendar, yet DAVdroid would re-add it at sync. If I delete it for 1 occurance in my local Android calendar, Horde would show it still but struck out.
Another scenario in that same thing, I modified a recurring event, same one, to have an end time. When android synced, it deleted the entire schedule.
There’s definitely some issues when dealing with recurring events, at least with Horde. I have yet to check this out in any other CalDAV server (such as I also use owncloud, but rarely sync with it anymore, mostly files).
I had to go back to using Marten Gajda’s CalDAV-Sync for the time being to resolve this issue temporarily, as it works, in that respect, fully without issues with recurring event calendars.
I have similar problems -but I’m using “Kolab Groupware”. If I create a recurring event and modify a single event of this set (e.g. change the name or the duration) then DavDroid does not Update/Sync this change to my mobile phone.
Further problems exist in the context of deleting a single event of such a row - I observe the same behavior as described by @erenfro
If you need more information -please let me know
Thanks for your report.
Duplicate of #170, please follow up there.