**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`
itRenders('false children as blank', async render => {
        const e = await render(<div>{false}foo</div>);
        expect(e.childNodes.length).toBe(1);
        expectTextNode(e.childNodes[0], 'foo');
      });
      itRenders('null and false children together as blank', async render => {
        const e = await render(<div>{false}{null}foo{null}{false}</div>);
        expect(e.childNodes.length).toBe(1);
        expectTextNode(e.childNodes[0], 'foo');
      });
      itRenders('only null and false children as blank', async render => {
        const e = await render(<div>{false}{null}{null}{false}</div>);
        expect(e.childNodes.length).toBe(0);
      });
    });
    describe('elements with implicit namespaces', function() {
      itRenders('an svg element', async render => {
        const e = await render(<svg />);
        expect(e.childNodes.length).toBe(0);
        expect(e.tagName).toBe('svg');
        expect(e.namespaceURI).toBe('http:www.w3.org/2000/svg');
      });
      itRenders('svg child element with an attribute', async render => {
        let e = await render(<svg viewBox="0 0 0 0" />);
        expect(e.childNodes.length).toBe(0);
        expect(e.tagName).toBe('svg');
        expect(e.namespaceURI).toBe('http:www.w3.org/2000/svg');
        expect(e.getAttribute('viewBox')).toBe('0 0 0 0');
      });
      itRenders(