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".
tagVerbatim,
  tagLowercase,
  props,
  namespace,
  makeStaticMarkup,
  isRootElement,
  instForDebug,
) {
  var ret = '<' + tagVerbatim;
  for (var propKey in props) {
    if (!props.hasOwnProperty(propKey)) {
      continue;
    }
    var propValue = props[propKey];
    if (propValue == null) {
      continue;
    }
    if (propKey === STYLE) {
      propValue = createMarkupForStyles(propValue, instForDebug);
    }
    var markup = null;
    if (isCustomComponent(tagLowercase, props)) {
      if (!RESERVED_PROPS.hasOwnProperty(propKey)) {
        markup = DOMMarkupOperations.createMarkupForCustomAttribute(
          propKey,
          propValue,
        );