Calendar Invitees not working (mostly).

I am getting inconsistent behavior using Calendar 5 and I'm not sure why. This is paired with Calendar Server using Mountain Lion Server.

Whenever our secretary sends out events to the entire office (using a group in Contacts.app which is pullling contacts from a network user on Lion Server) nobody gets them. If she sends to invites to people in that group individually, they do get it.

Here's what I've found from my own testing:

1) Create group on server using Server.app, add network users to that group, send invite to that group from Calendar.app on client computer = works great

2) Create shared group* on client computer Contacts.app, add users to group in Contacts.app, send invite to that group from Calendar.app on client computer = works sometimes, sometimes doesn't work

*Shared group and users in group comes from server network user account we all have access to in our Contacts.app preferences.

3) Create shared group on client computer Contacts.app, add users to group in Contacts.app, send invite to that group from Calendar.app on client computer = works sometimes, sometimes doesn't work

4) Create shared group on client computer Contacts.app, add add single user to group in Contacts.app (whose name appears with question mark by it in Calendar.app no matter what time for the event), send invite to that group from Calendar.app on client computer = recipient does not get invite*

*Recipient is using iCal in Lion, but this was not an issue before Mountain Lion.

Setup

1. Mac Mini Server with Mountain Lion Server
2. Client computers with Lion and Mountain Lion (iCal and Calendar, AddressBook and Contacts)
3. Server-side user account established strictly for creating/ adding shared contacts from client AddressBook.app/ Contacts.app; shared by everyone having access to that account in AddressBook.app/ Contacts.app account preferences.
4. Server-side users that I added to a group using Server.app were the same users with the same primary email address as the users and groups used in Contacts.app that Calendar.app referenced. I made sure to create unique group names so that when adding invitees I knew whether the group was created server-side or created server-side through the client-side Contacts.app