[turba] CardDAV: Contacts don't show up in eMClient or Thunderbird, but *writing* contacts works

[Natanji]

Hi,
quickly want to ask around here before I file a bug report. I'm on Horde
5.1.3 and trying to access my adress book via CardDAV. This works
perfectly fine on my Android with the "CardDav Sync" app, but it doesn't
work completely in eM Client nor in Thunderbird with Inverse SOGo Connector.

By "completely" I mean that I can *write* entries to the adress boook
and they show up on the server just fine. So the authentication and
connection to Horde definitely works. And in the logfiles I can
definitely see that Horde is sending the contact data back. But the
response that Horde generates seems to not be understood by the Client;
perhaps it is not correctly formatted. The problem is also documented
here (with logfiles):
http://forum.emclient.com/emclient/topics/carddav_server_contacts_not_showing_in_em_but_when_we_create_contact_on_em_it_is_getting_synced_on_carddav

If this is a problem in SabreDAV, it would be a regression: I have
another server with OwnCloud 5 installed, which uses SabreDAV 1.7.6, and
syncing contacts via CardDAV works perfectly fine there. On Horde 5.1.3
we have SabreDAV 1.8.7 so that's *much* more up to date, and it does not
work there.

I was not able to find any bug in Horde or SabreDAV that sounds like
this, and I don't even know if it's a bug in the sense that
Horde/SabreDAV go against the CardDAV specification (which the eM Client
developers claim) or if it's a bug in the clients I tested. I just
figured I would try here first since it seems weird that multiple
completely different clients would have the same issue.

Any input on what to do would be greatly appreciated.

Cheers,
Natanji