Version

3.0.3

Reproduction link

https://codesandbox.io/s/elastic-christian-33req?file=/src/components/GrandChild.vue

Steps to reproduce

1. Open https://codesandbox.io/s/elastic-christian-33req?file=/src/components/GrandChild.vue
2. Observe double alert from App and Child components

What is expected?

Alert only from Child

What is actually happening?

Alert from App and Child

As I understood it is not a bug, more like a caveat, so it would be cool to have detailed explanation of what is happening in docs

You need inheritAttrs: false in Child.vue. This is documented: https://v3.vuejs.org/guide/component-attrs.html#attribute-inheritance

It is. But isn't it unexpected that listeners are explicitly bound to wrong component?

No, you have to either disable attribute inheritance or declare the emits option https://v3.vuejs.org/guide/migration/emits-option.html