**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.

if (key === flushedKey) {
        
        return;
      }
      expect(this.refs[key]).toBeTruthy();
    }
  },
  render: function() {
    var children = [];
    var key;
    for (key in this.props.usernameToStatus) {
      var status = this.props.usernameToStatus[key];
      children.push(
        !status ? null :
        <StatusDisplay
          key={key}
          ref={key}
          onFlush={this.verifyPreviousRefsResolved.bind(this, key)}
          status={status}
        />
      );
    }
    return (
      <div>
        {children}
      </div>
    );
  },
});
function getInternalStateByUserName(statusDisplays) {