**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`
if (!container) {
    return null;
  }
  if (container.nodeType === DOCUMENT_NODE) {
    return container.documentElement;
  } else {
    return container.firstChild;
  }
}
function shouldHydrateDueToLegacyHeuristic(container) {
  const rootElement = getReactRootElementInContainer(container);
  return !!(rootElement &&
    rootElement.nodeType === ELEMENT_NODE &&
    rootElement.hasAttribute(ROOT_ATTRIBUTE_NAME));
}
function shouldAutoFocusHostComponent(type: string, props: Props): boolean {
  switch (type) {
    case 'button':
    case 'input':
    case 'select':
    case 'textarea':
      return !!props.autoFocus;
  }
  return false;
}
var DOMRenderer = ReactFiberReconciler({
  getRootHostContext(rootContainerInstance: Container): HostContext {
    let type;