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

**What is the current behavior?**
I've started recieving this warning about my SVGs which is using [feGaussianBlur](https://developer.mozilla.org/en-US/docs/Web/SVG/Element/feGaussianBlur): 
`Warning: Expected server HTML to contain a matching <feGaussianBlur> in <filter>.`

**What is the expected behavior?**
Should be no warnings because there are no difference.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
Such behavior started right after updating to `React 16.0.0-rc.3` and never happened with `React 15.6.1`
}
    const isRootRenderedBySomeReact = !!container._reactRootContainer;
    const rootEl = getReactRootElementInContainer(container);
    const hasNonRootReactChild = !!(rootEl &&
      ReactDOMComponentTree.getInstanceFromNode(rootEl));
    warning(
      !hasNonRootReactChild || isRootRenderedBySomeReact,
      'render(...): Replacing React-rendered children with a new root ' +
        'component. If you intended to update the children of this node, ' +
        'you should instead have the existing children update their state ' +
        'and render the new components instead of calling ReactDOM.render.',
    );
    warning(
      container.nodeType !== ELEMENT_NODE ||
        !((container: any): Element).tagName ||
        ((container: any): Element).tagName.toUpperCase() !== 'BODY',
      'render(): Rendering components directly into document.body is ' +
        'discouraged, since its children are often manipulated by third-party ' +
        'scripts and browser extensions. This may lead to subtle ' +
        'reconciliation issues. Try rendering into a container element created ' +
        'for your app.',
    );
  }
  let root = container._reactRootContainer;
  if (!root) {
    const shouldHydrate =
      forceHydrate || shouldHydrateDueToLegacyHeuristic(container);
    
    if (!shouldHydrate) {
      let warned = false;