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.
to.dispatchEvent(
          new MouseEvent('mouseover', {
            bubbles: true,
            cancelable: true,
            relatedTarget: from,
          }),
        );
      }
    }
    try {
      ReactDOM.render(
        <div>
          <div
            onMouseEnter={() => ops.push('enter parent')}
            onMouseLeave={() => ops.push('leave parent')}>
            <div ref={n => (firstTarget = n)} />
            {ReactDOM.createPortal(
              <div
                onMouseEnter={() => ops.push('enter portal')}
                onMouseLeave={() => ops.push('leave portal')}
                ref={n => (secondTarget = n)}>
                portal
              </div>,
              portalContainer,
            )}
          </div>
          <div ref={n => (thirdTarget = n)} />
        </div>,
        container,
      );