Actually, I'm able to connect to

davs://ampoliros.net/iRony/addressbooks/

and then I can nevigate back to 

davs://ampoliros.net/iRony/

-> gvfs

Sounds like an issue with the gvfs WebDav backend. There have been a bunch of fixes related to that recently; what version of gvfs are you using?

gvfs-info --version
gvfs 1.22.2

Thanks for the report. I have tested connecting to a Kolab 3.3 server with gvfs 1.22 using davs and it worked fine for me.

Please run the following in a terminal:
pkill gvfs; GVFS_DEBUG=all GVFS_HTTP_DEBUG=all `find /usr/lib* -name 'gvfsd'` &> ~/log.txt

Then attempt to mount the share, reproduce the problem, and then upload log.txt in your home directory so we can see a log of what is happening.  If possible, it would be good if you could do it using the gvfs command-line tools; e.g. gvfs-mount davs://ampoliros.net/iRony/

Thanks. Here's the log:

    Added new job source 0xa6a330 (GVfsBackendDav)
    Queued new job 0xa82380 (GVfsJobMount)
    + mount
    > OPTIONS /iRony HTTP/1.1
    > Soup-Debug-Timestamp: 1416296116
    > Soup-Debug: SoupSession 1 (0xa86150), SoupMessage 1 (0x7f760c0058b0), SoupSocket 1 (0x7f7614006e90)
    > Host: ampoliros.net
    > Accept-Encoding: gzip, deflate
    > User-Agent: gvfs/1.22.2
    > Accept-Language: fr-fr, fr;q=0.9
    > Connection: Keep-Alive
      
    < HTTP/1.1 200 OK
    < Soup-Debug-Timestamp: 1416296116
    < Soup-Debug: SoupMessage 1 (0x7f760c0058b0)
    < Date: Tue, 18 Nov 2014 07:35:19 GMT
    < Server: Apache/2.2.22 (Debian)
    < Allow: OPTIONS,GET,HEAD,POST
    < Content-Length: 0
    < Keep-Alive: timeout=5, max=100
    < Connection: Keep-Alive
    < Content-Type: httpd/unix-directory
    < 
      
    send_reply, failed: 1

    ** (gvfsd:29721): WARNING **: dbus_mount_reply: Error from org.gtk.vfs.Mountable.mount(): Ce partage ne prend pas en charge WebDAV

The web server is misconfigured. It does not reply with a "DAV" header, so gvfs assumes that it is not a webdav share (the error is "Not a WebDAV enabled share").

From the RFC for WebDAV: """All DAV compliant resources MUST return the DAV header on all OPTIONS responses."""
The web server is thus not being a compliant webdav server.

I guess that the Apache configuration is stripping the header away (mod_header maybe?).

Thanks, then I'll file the bug with Kolab… I wonder it works with other clients I have tried (KDE Dolphin, Mac OS X Finder)

It may be a simple configuration issue or particular to Debian, since it worked fine with me on CentOS 7 and Kolab 3.3.

As for why it worked with other clients, perhaps they're not as strict?

FYI, it works if I connect to davs://ampoliros.net/iRony/index.php instead of just davs://ampoliros.net/iRony/