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.
{usePortal(<div {...expectHTML} />)}
        <image {...expectSVG} />
        {usePortal(<div {...expectHTML} />)}
        <image {...expectSVG} />
      </svg>,
    );
    assertNamespacesMatch(
      <div {...expectHTML}>
        <math {...expectMath}>
          <mi {...expectMath} />
          {usePortal(
            <svg {...expectSVG}>
              <image {...expectSVG} />
            </svg>,
          )}
        </math>
        <p {...expectHTML} />
      </div>,
    );
    assertNamespacesMatch(
      <math {...expectMath}>
        <mi {...expectMath} />
        {usePortal(
          <svg {...expectSVG}>
            <image {...expectSVG} />
            <foreignObject {...expectSVG}>
              <p {...expectHTML} />
              <math {...expectMath}>
                <mi {...expectMath} />
              </math>