Kolab 3.3: Roundcube Files Tab non-functional?

[Johannes Graumann]

Hello,

My 3.3 setup (Enterprise edition) works like a charm, however the "Files"
tab in roundcube is non functional:
- There is a "Files" folder in my imap hierarchy, which is marked as type
"files" and the default location;
- https://<MYSERVER>/chwala/ allows me to log on and operate
- Choosing the File tab in roundcube shows me the empty infrastructure. If I
try to add a folder everything freezes and nothing happens.

I have tried prowling the logs for info, but have come up empty. What ports
URLs must be accessible for this to work? Maybe its firewalling/nginx proxying?

Any hint is highly appreciated.

Sincerely, Joh