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I noticed that an admin having permission to modify users but that can only handle a few roles, changing a user having a role different from those ones he can change, inevitably the role of the changed user changes.
For example, adding the "Manager" role that can only handle "Member" and "Editor" roles, if he changes a manager (including himself) his role (field "type") changes.
If a "Manager" could see and edit only users with a role that he can manage, could be a solution? He would not see himself in the users administration page (/user/admin) but he could change his profile through /user/update page, that already does not involve editing the role.