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.
portalContainer1,
        ),
        <div key="f">normal[1]</div>,
      ],
      container,
    );
    expect(portalContainer1.innerHTML).toBe(
      '<div>portal1[0]</div><div>portal1[1]</div>',
    );
    expect(portalContainer2.innerHTML).toBe('<div>portal2[0]</div>');
    expect(portalContainer3.innerHTML).toBe('<div>portal3[0]</div>');
    expect(container.innerHTML).toBe(
      '<div>normal[0]</div><div>normal[1]</div>',
    );
    ReactDOM.unmountComponentAtNode(container);
    expect(portalContainer1.innerHTML).toBe('');
    expect(portalContainer2.innerHTML).toBe('');
    expect(portalContainer3.innerHTML).toBe('');
    expect(container.innerHTML).toBe('');
  });
  it('should reconcile portal children', () => {
    const portalContainer = document.createElement('div');
    ReactDOM.render(
      <div>{ReactDOM.createPortal(<div>portal:1</div>, portalContainer)}</div>,
      container,
    );
    expect(portalContainer.innerHTML).toBe('<div>portal:1</div>');
    expect(container.innerHTML).toBe('<div></div>');
    ReactDOM.render(
      <div>{ReactDOM.createPortal(<div>portal:2</div>, portalContainer)}</div>,