Inconsistency with native behavior

[ghost]

import "./polyfill.mjs"

let x = JSON.parse(`{
   "__proto__" : null
}`)

let y = JSON.parse(`{
   "__proto__" : null
}`, (key, value, context) => value)

console.assert(
    Object.getOwnPropertyNames(x).length == Object.getOwnPropertyNames(y).length
)

Expected: Assertion ok
Actually: Assertion failed