In CMS administration > users, groups and rights tab > Application groups group:

1. Create 2 group directories based on the same datasource.
2. Create a group on one of these directories: 2 lines appear in groups list with same group identifier. It seems that there is only one group but one line per group directory. => OK (I think)
3. Select one line and click on delete button: only the selected line disappears. => KO
4. Select the other line and click on rename or delete button: An error occurs, the group does not exist anymore => KO