New object prop bypasses React.memo

What does this output?

function shallowEqual(a, b) {
  return Object.keys(a).every(k => a[k] === b[k]) &&
         Object.keys(b).every(k => b[k] === a[k]);
}

let renders = 0;
function memo(Component) {
  let prev = null;
  return (props) => {
    if (prev && shallowEqual(prev, props)) { return 'skipped'; }
    prev = props;
    renders++;
    return Component(props);
  };
}

const List = ({ items }) => 'list:' + items.join(',');
const MemoList = memo(List);

const stableItems = [1, 2, 3]; // defined outside

console.log(MemoList({ items: stableItems }));  // render
console.log(MemoList({ items: stableItems }));  // skip — same ref
console.log(MemoList({ items: [1, 2, 3] }));    // render — new array!
console.log(renders);

Correct Output

list:1,2,3
skipped
list:1,2,3
2

Why this output?