WP_User::set_role() does not remove previous roles

[fried_eggz]

If a user has a role that has been removed from WordPress by using remove_role() this role is not removed when using WP_User::set_role() on the user.

Example:

remove_role('subscriber') has been used on the install removing the subscriber role from available roles.

A new user is created with wp_create_user()

The new user is automatically assigned the role subscriber (which does not exist)

The new users role is set using WP_User::set_role()

In the database, the usermeta row with capabilities for the new user still contains the subscriber role and the new role is given an index of 1 instead of 0 in the $user->roles array.

Expected result:

WP_User::set_role() should effectively remove all previous roles from the user even if they have been removed from WordPress with remove_role().