Why the initial data is being updated before it is changed? And how to fix it?

[Lonest90]

I am facing a problem, the initialData which is an array is being updated within the mutate by a clone array.

React.JS (After update the page): https://codesandbox.io/s/swr-mutate-bug-forked-6zf9k?file=/src/index.tsx
Next.JS: https://codesandbox.io/s/priceless-goldwasser-6qnvx?file=/pages/index.js

The mutation:

const { data, error, mutate } = useSWR("foo", () => [
    { id: 1, title: "Foo 1" },
    { id: 2, title: "Foo 2" }
])

mutate((oldData) => {
    const _data = [...oldData]
    console.log(data) //The output
    _data.find((e) => e.id === 2).title = "Foo mutated"
    return _data
}, false)

Output (console.log):

And finally, the mutate doesn’t render because it has already been updated, kind of confusing. What can i be doing wrong?

Note: This happens after updating the page in React.JS and Next.JS it happens all the time