**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`
return !!(node &&
    (node.nodeType === ELEMENT_NODE ||
      node.nodeType === DOCUMENT_NODE ||
      node.nodeType === DOCUMENT_FRAGMENT_NODE ||
      (node.nodeType === COMMENT_NODE &&
        node.nodeValue === ' react-mount-point-unstable ')));
}
function getReactRootElementInContainer(container: any) {