**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`
render === serverRender ||
            render === streamRender ||
            render === clientRenderOnServerString
          ) {
            
            
            
            expect(e.title).toBe('foo\nbar\nbaz\nqux\uFFFD');
          } else {
            
            expect(e.title).toBe('foo\rbar\r\nbaz\nqux\u0000');
          }
        },
      );
    });
    describe('components that throw errors', function() {
      itThrowsWhenRendering(
        'a function returning undefined',
        async render => {
          const UndefinedComponent = () => undefined;
          await render(<UndefinedComponent />, 1);
        },
        'UndefinedComponent(...): Nothing was returned from render. ' +
          'This usually means a return statement is missing. Or, to ' +
          'render nothing, return null.',
      );
      itThrowsWhenRendering(
        'a class returning undefined',
        async render => {
          class UndefinedComponent extends React.Component {