I thought this was a one off when first reported to me, but after a few more calls about this and testing it out myself this is what i'm finding:

User A shares their address book with User b. Within this shared address book, there are contacts and groups.
User B makes a change to the group within the shared address book (say, adds a user).
User A does not see the change in the group.
User A then adds a user to the group. User B does not see the changes.

Running GW 802Hp2 1/8/2011 Build 92614 on both clients.

Backend is GW802HP2 on SUSE 10 SP3.
Both users are in different post offices but the same domain.

Anyone else having this issue?