**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`
return null;
        }
        const e = await render(
          <div>
            {[['a'], 'b']}
            <div>
              <X key="1" />
              d
            </div>
            e
          </div>,
        );
        if (
          render === serverRender ||
          render === clientRenderOnServerString ||
          render === streamRender
        ) {
          
          expect(e.childNodes.length).toBe(5);
          expectTextNode(e.childNodes[0], 'a');
          expectTextNode(e.childNodes[2], 'b');
          expect(e.childNodes[3].childNodes.length).toBe(3);
          expectTextNode(e.childNodes[3].childNodes[0], 'c');
          expectTextNode(e.childNodes[3].childNodes[2], 'd');
          expectTextNode(e.childNodes[4], 'e');
        } else {
          expect(e.childNodes.length).toBe(4);
          expectTextNode(e.childNodes[0], 'a');