Before 1.9 it used to be one "Roles" tab having two possibilities in the second row (roles and overrides/permissions).
That was changed for > 1.9 but with the change, support for a real second row was completely dropped.
So I'm going to perform some really minor changes in admin/roles/tabs.php to re-introduce support to that second row that was previously there (in fact I've one module currently using that second row feature via the "extratabs" extension) and I think it's good to have such support there.
It won't modify the rest of tabs (update, roles and permissions) at all. Just extratabs will be able to declare a second row.