Observed this on react@16.0.0-beta.5

```js
import React from 'react';
import { renderToString } from 'react-dom/server';

const B = () => 'b';

console.log(renderToString(<div>{'a'}<B />{'c'}</div>));
```

This renders as `<div data-reactroot="">a<!-- -->bc</div>`. If you try to hydrate this you'll get the error: Text content did not match. Server: "bc" Client: "b".
publicInstance: ReactComponent<any, any, any>,
  callerName: string,
) {
  if (__DEV__) {
    var constructor = publicInstance.constructor;
    warning(
      false,
      '%s(...): Can only update a mounting component. ' +
        'This usually means you called %s() outside componentWillMount() on the server. ' +
        'This is a no-op.\n\nPlease check the code for the %s component.',
      callerName,
      callerName,
      (constructor && getComponentName(constructor)) || 'ReactClass',
    );
  }
}
function shouldConstruct(Component) {