Ok I had some time to investigate what I discovered (in comment 68). Still not sure if it's the cause of this bug but I am now able to reliably reproduce a serious similar bug:
1. launch users-admin
2. create a test1 user
3. create a test2 user (with admin rights)
4. create a test3 user
5. delete the test1 user
6. delete the test3 user
Here you go, test2 is no longer in the admin groups.
Ok I had some time to investigate what I discovered (in comment 68). Still not sure if it's the cause of this bug but I am now able to reliably reproduce a serious similar bug:
1. launch users-admin
2. create a test1 user
3. create a test2 user (with admin rights)
4. create a test3 user
5. delete the test1 user
6. delete the test3 user
Here you go, test2 is no longer in the admin groups.
I opened a bug upstream where I put a detailed explanation: http:// bugzilla. gnome.org/ show_bug. cgi?id= 489187