[horde] ActiveSync duplicate events

[Philipp Faeustlin]

I found some new strange behaviour between Horde and ActiveSync devices.
Events created via activesync are synced to horde calender and then back 
to the activesync device.
I end up with 2 events on the activesync device and one in webmail.

Removing on of the events on the device, I'll end up with no event in 
webmail and the duplicate on the device is also removed.

Removing the event in webmail, one of the events on the device will be 
removed the other one stays.

On the activesync device on which I create the new event I will have two 
events visible after syncing, the second device has only one event visible.

My test system is:
Horde 5.2.15
Horde_ActiveSync 2.31.9
Kronolith 4.2.16

Activesync Devices:
SAMSUNG - Android 5.0.1 - EAS Verion 14.1
WindowsOutlook15 - Outlook/15.0 - EAS Verion 14.0

Any suggestions how to solve that problem?

Regards
Philipp