The query for K2-Steps-14 is:

<r>
    {
        let $i :=   <e>
                        <a/>
                        <b/>
                    </e>
        let $b := ($i/b, $i/a, $i/b, $i/a)
        return ()/$b
    }
</r>

The expected result for this query is <r><a/><b/></r>. I believe that ()/$b should produce (), and so I believe that the expected result should be <r/>.