I'm able to create a usergroup and add users to it but, when I edit a user group I get 2 items on my screen :

--------------
"User Groups" 
<empty>
----and-------
"Users" 
AdminUser , UserA, UserB etc
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There's no option to edit rights/roles of this group. I believe what we should expect here is something like this:

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"User Groups" 
<in case nested groups are supported>
----and-------
"Roles" 
<Where you could select which role this usergroup gets>
----and-------
"Users" 
AdminUser , UserA, UserB etc
--------------