i have this problem with actually (DAVdroid 0.8.4.1) .
I have this problem with the Motorola Moto G and a Ford car radio .
With the old firmware (Android 4.4) and CardDAV-Sync ist works, i could use the adressbook with the car radio.
After the update (Android 5.02) i switched to davdroid and now it don’t work. I could not use the adressbook with the car radio.
All other is working (connection handy <> car radio par examle with the outgoing an incoming calls…)
What can i do? What can i check?