Hello again,
here is a DAVdroid log/trace from the smartphome:
0_1453799194399_davdroid-SyncManager-Kalender olli-com.android.calendar.txt
On the smartphone I changed a event titled “Test” to 20:30 o’clock. Im in GMT+1 (Europe/Berlin).
After the sync to Horde the time in my phone and Horde changed do 19:30.