**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 {text2: 'red'};
        }
        render() {
          return <Grandchild />;
        }
      }
      Child.childContextTypes = {text2: PropTypes.string};
      const Grandchild = (props, context) => {
        return (
          <div>
            <div id="first">{context.text1}</div>
            <div id="second">{context.text2}</div>
          </div>
        );
      };
      Grandchild.contextTypes = {
        text1: PropTypes.string,
        text2: PropTypes.string,
      };
      const e = await render(<Parent />);
      expect(e.querySelector('#first').textContent).toBe('purple');
      expect(e.querySelector('#second').textContent).toBe('red');
    });
    itRenders(
      'with a call to componentWillMount before getChildContext',
      async render => {
        class WillMountContext extends React.Component {