Extracted from https://github.com/facebook/react/issues/12643.

We're currently diff a host node in the complete phase even if it has bailed out in the begin phase. By itself, this just means we're doing a little bit more work than necessary. But it also has some observable effects. In particular, https://github.com/facebook/react/issues/13424 (which by itself would be very rare and probably not worth fixing) is made worse because we end up committing update to inputs from another component.

I have a fix for this in https://github.com/facebook/react/pull/13423. Filing this for posterity.
assertNamespacesMatch(
      <svg {...expectSVG}>
        <image {...expectSVG} />
        {usePortal(<div {...expectHTML} />)}
        <image {...expectSVG} />
      </svg>,
    );
    assertNamespacesMatch(
      <math {...expectMath}>
        <mi {...expectMath} />
        {usePortal(<div {...expectHTML} />)}
        <mi {...expectMath} />
      </math>,
    );
    assertNamespacesMatch(
      <div {...expectHTML}>
        <p {...expectHTML} />
        {usePortal(
          <svg {...expectSVG}>
            <image {...expectSVG} />
          </svg>,
        )}
        <p {...expectHTML} />
      </div>,
    );
  });
  it('should keep track of namespace across portals (medium)', () => {
    assertNamespacesMatch(
      <svg {...expectSVG}>
        <image {...expectSVG} />