Version

3.0.5

Reproduction link

https://jsfiddle.net/57no3akz/9/

Steps to reproduce

const {shallowReadonly, isProxy} = Vue

let origin = new Map([[1, {a: 1}]])

let proxy = shallowReadonly(origin)

console.log(isProxy(proxy.get(1)))

What is expected?

return the origin object

What is actually happening?

return the proxy of the origin object

See https://github.com/vuejs/vue-next/pull/3003