**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`
containerNode: DOMContainer,
    callback: ?Function,
  ) {
    invariant(
      parentComponent != null && ReactInstanceMap.has(parentComponent),
      'parentComponent must be a valid React Component',
    );
    return renderSubtreeIntoContainer(
      parentComponent,
      element,
      containerNode,
      false,
      callback,
    );
  },
  unmountComponentAtNode(container: DOMContainer) {
    invariant(
      isValidContainer(container),
      'unmountComponentAtNode(...): Target container is not a DOM element.',
    );
    if (container._reactRootContainer) {
      if (__DEV__) {
        const rootEl = getReactRootElementInContainer(container);
        const renderedByDifferentReact =
          rootEl && !ReactDOMComponentTree.getInstanceFromNode(rootEl);
        warning(
          !renderedByDifferentReact,
          "unmountComponentAtNode(): The node you're attempting to unmount " +
            'was rendered by another copy of React.',
        );