Version

3.2.0-beta.7

Reproduction link

https://codesandbox.io/s/serene-haze-f86nw?file=/src/App.vue:328-339

Steps to reproduce

1. create a customMyRef
2. use isRef to customMyRef
3. ouput isRef result

What is expected?

the result is false

What is actually happening?

the result is true

You are not supposed to add a property named __v_isRef to your object. It's also completely unrealistic use case