"Missing React element for debugID" warning when triggering a render in componentWillMount

[yannickcr]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
As reported by @adamryvola in #6869 (comment), React is displaying a warning Warning: ReactComponentTreeDevtool: Missing React element for debugID 2 when building stack when another component is rendered in componentWillMount

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem via https://jsfiddle.net or similar (template: https://jsfiddle.net/reactjs/69z2wepo/).

import React, {Component} from 'react';
import ReactDOM from 'react-dom';

const container = document.getElementById('container');
const menuContainer = document.getElementById('menu-container');

export default class App extends Component {

  componentWillMount() {
    ReactDOM.render(<div />, menuContainer);  // <= Trigger the warning
  }

  render() {
    return (
      <div>
        <div>App</div>
      </div>
    );
  }
}

ReactDOM.render(<App />, container);

JSFiddle: https://jsfiddle.net/0n3a6vp9/

What is the expected behavior?
According to @gaearon this warning is "against internal bugs in React, it's not meant for users" (source: #6869 (comment)) so this warning should not be triggered.

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?
React 15.2.0, no issue with React 0.14.7

[gaearon]

Interestingly, also appears triggered by ReactDOMServer usage inside render: #7190

[gaearon]

Okay, #7193 should fix it.

[gaearon]

Fixed by #7193.

[adamryvola]

Hello,
i created small project. It gives me this warring. Here is link: small-kit

Please, can you try it, and tell me, where is the problem? I cant find it.

I am very thankful for all your help!

[gaearon]

This is a bug in React and it should be fixed in master.
Please wait for the next release.
If it's not fixed for you in the next release, please file another issue.

[angusfretwell]

Hey,

I'm still getting this warning (specifically Warning: ReactComponentTreeDevtool: Missing React element for debugID X when building stack) when running tests with Jest.

[gaearon]

File an issue with the code reproducing it. Thank you!