Tested with SOGo 1.3.7 in the Webinterface.
While giving rights to another user on a calendar with "Sharing..", you have to give this user some right!

You can set all levels "Public", "Confidential" and "Private" to "None", but you have to set either "This person can create objects in my calendar." or "This person can erase objects from my calendar.".

You only can set all but one of "Public", "Confidential" and "Private" to "None" while "This person can create objects in my calendar." and "This person can erase objects from my calendar." are not set.

If you try to set all to "None", then after "Update" security levels "Public" and "Confidential" get set to "View the Date & Time".
So you not only can't set all three to "None", you even get a totally wrong setting!

A user who wants to revoke all rights will be surprised to see the result.
There should at least be an error message in this case.

Workaround:
Delete the user in question from the calendar sharing list to remove all rights from her.

Try to restart memcached between tests. I'm pretty sure the cache isn't updated properly right away.

Try the following patch:

============================================================
--- SoObjects/SOGo/SOGoGCSFolder.m 075ea8f10b351cafb9c69aab74512b16a263f9c8
+++ SoObjects/SOGo/SOGoGCSFolder.m 00268a7356b2255bd9d593b990a0c053fbf3f7ee
@@ -1637,11 +1637,13 @@ static NSArray *childRecordFields = nil;
[newRoles removeObject: SOGoRole_AuthorizedSubscriber];
[newRoles removeObject: SOGoRole_None];
objectPath = [objectPathArray componentsJoinedByString: @"/"];

• [self _cacheRoles: newRoles forUser: uid

• forObjectAtPath: objectPath];

• if (![newRoles count])
  [newRoles addObject: SOGoRole_None];

• [self _cacheRoles: newRoles forUser: uid

• forObjectAtPath: objectPath];

• [self _commitRoles: newRoles forUID: aUID forObject: objectPath];
  }

Yes, this patch solves problem on my server.

Thanks

Fixed with: http://mtn.inverse.ca/revision/diff/fa2e7098c9457bb1b9933f49556578b5326860d2/with/5be507aec21eb7c99a5024135035b80901450a40