We switched the logic for what shows in the Audience form element when a non admin edits a group post. Now the groups belonging to the current user are shown, along with the nodes that the group already has. Before, we showed the groups of the node author. This was a bug fix that became critical with the introduction of private groups. See http://drupal.org/node/164070.
Note that the structure of #options has changed in the Audience form element. You might be affected if you form_alter the options of that element.