**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`
getChildContext() {
            return {text: this.state.text};
          }
          componentWillMount() {
            this.setState({text: 'foo'});
          }
          render() {
            return <Child />;
          }
        }
        WillMountContext.childContextTypes = {text: PropTypes.string};
        const Child = (props, context) => {
          return <div>{context.text}</div>;
        };
        Child.contextTypes = {text: PropTypes.string};
        const e = await render(<WillMountContext />);
        expect(e.textContent).toBe('foo');
      },
    );
    itThrowsWhenRendering(
      'if getChildContext exists without childContextTypes',
      render => {
        class MyComponent extends React.Component {
          render() {
            return <div />;
          }
          getChildContext() {