**Do you want to request a _feature_ or report a _bug_?**

Report a bug.

**What is the current behavior?**

When testing components, `Warning: ReactComponentTreeDevtool: Missing React element for debugID 1 when building stack` is shown when calling `TestUtils.renderIntoDocument`.

**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/).**

https://github.com/angusfretwell/reproduce-debugid-warning (`npm install && npm test`).

**What is the expected behavior?**

According to #7187 this is an internal warning and shouldn't be displayed.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
- react@15.2.1
- react-addons-test-utils@15.2.1
- react-dom@15.2.1

I didn't receive this warning on 15.2.0.

* Child key names are wrapped like '.$key:0'. We strip the extra chars out
 * here. This relies on an implementation detail of the rendering system.
 */
var getOriginalKey = function(childName) {
  var match = childName.match(/^\.\$([^.]+)$/);
  expect(match).not.toBeNull();
  return match[1];
};
/**
 * Contains internal static internal state in order to test that updates to
 * existing children won't reinitialize components, when moving children -
 * reusing existing DOM/memory resources.
 */
var StatusDisplay = React.createClass({
  getInitialState: function() {
    return {internalState: Math.random()};
  },
  getStatus: function() {
    return this.props.status;
  },
  getInternalState: function() {
    return this.state.internalState;
  },
  componentDidMount: function() {
    this.props.onFlush();
  },
  componentDidUpdate: function() {
    this.props.onFlush();
  },
  render: function() {