**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 newRoot = DOMRenderer.createContainer(container);
    root = container._reactRootContainer = newRoot;
    
    DOMRenderer.unbatchedUpdates(() => {
      DOMRenderer.updateContainer(children, newRoot, parentComponent, callback);
    });
  } else {
    DOMRenderer.updateContainer(children, root, parentComponent, callback);
  }
  return DOMRenderer.getPublicRootInstance(root);
}
function createPortal(
  children: ReactNodeList,
  container: DOMContainer,
  key: ?string = null,
) {
  invariant(
    isValidContainer(container),
    'Target container is not a DOM element.',
  );
  
  return ReactPortal.createPortal(children, container, null, key);
}
var ReactDOMFiber = {
  createPortal,
  findDOMNode(
    componentOrElement: Element | ?React$Component<any, any>,
  ): null | Element | Text {
    if (__DEV__) {