To reproduce the bug it is needed to have a Moodle 1.8 "pre group patch" from Petr Skoda. Using this older Moodle version:
1. create orphaned groups in a course
2. update Moodle with the latest 1.8 CVS version containing Petr's group fixes
3. in the same course of point #1 go to the Groups page: orphaned groups does not show, thus cannot be edited.
New groups can be created and people assigned to them. Orphaned groups are still functioning correctly across all course's activities, but there is no way to edit them.