hmm this seem to be a regression 
i’ll investigate...
EDIT :
Found an error in suppling the two UserSources dictionaries, but still not working;
not so sure it's a regression of sogo.conf, not working on my ns6 "reference" system.
expected behavior:
log in to SOGo with one user (let's say user1) and select Address Book (or Calendar) menu;
share user1's personal address book (or personal calendar) with a group (let's say testgroup) giving at least read permission;
log user1 out;
log in to SOGo again with a different user whom belongs to testgroup group (let's say user2) ;
try to ubscribe user1's shared address book (or calendar)
Can someone confirm this works on ns6?