Groups with members are being successfully published, however if the target environment administrator adds some target members to those groups, they will disappear over a given time.
What can be done to avoid this?
This is by design of QCS security model, only group owner can change group membership. In this case only the publisher (publishing side) can change the membership. All changes made manually on subscribing side will be overwritten.
The correct way to resolve such a problem is to publish the required member objects back to the side where original group resides, and then include the stub objects into the group there.
When such group is published, on the subscribers side, those stub members will be substituted with real users.
For more information please see Synchronized Groups feature description in QCS 2.0 What's New.