"Root" role does not have permissions to recreate oplog

I am running into an issue with the 3.2.12 server

I have a user with 'root' role that is not able to recreate the oplog ( in order to scale up the size of the oplog)

> db.runCommand({ create: "oplog.rs", capped: true, size: 1503238553.0 })

{

	"ok" : 0,

	"errmsg" : "not authorized on local to execute command { create: \"oplog.rs\", capped: true, size: 1503238553.0 }",

	"code" : 13

}

If the user is granted readWrite on the local DB then it starts to work

 db.grantRolesToUser("admin", [{role: "readWrite", db: "local"}])

Is this expected? I would expect the 'root' role to be a superset of all the permissions.