Variables starting with _ causes warning: "not defined on the instance but referenced during render"

[lsdsjy]

Version

2.7.0-beta.8

Reproduction link

codesandbox.io

Steps to reproduce

See console output

What is expected?

One warning:
Avoid using variables that start with _ or $ in setup().

(Like in Vue 3)

What is actually happening?

Two warnings:

Avoid using variables that start with _ or $ in setup().

Property or method "_a" is not defined on the instance but referenced during render. Make sure that this property is reactive, either in the data option, or for class-based components, by initializing the property.

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I think the second warning may be redundant.

[yyx990803]

This is fine since both warnings make sense and they do not affect behavior.