Consider the following XML document:

<article>
  <front>
    <article-meta>
      <aff id="aff1">Tropical and Infectious Disease Hospital, Kathmandu, Nepal</aff>
      <aff id="aff2">Nagasaki University, Nagasaki, Japan</aff>
      <aff id="aff3">Department of  Radiology, Kyorin University Faculty of Medicine, Tokyo, Japan</aff>
      <aff id="aff5">Pentax Company Limited, Tokyo, Japan</aff>
      <aff id="aff6">National  Research  Laboratory  of Molecular  Complex  Control, Yonsei University, Seoul, Korea</aff>
      <!--* ... *-->
      <article-id pub-id-type="pmc">2570825</article-id>
      <article-id pub-id-type="pmid">18325280</article-id>
      <article-id pub-id-type="publisher-id">07-0473</article-id>
      <article-id pub-id-type="doi">10.3201/eid1403.070473</article-id>
    </article-meta>
  </front>
  <!--* ... *-->
</article

For convenience in trying to understand this problem, a copy of this
document has been placed at [1].

When I issue the following search against this document, I get
unexpected results.

let $doc := doc('http://blackmesatech.com/2014/LIS590DML/data/testdata.xml')

let $path1 := $doc/child::article/child::front
              /child::article-meta
              /child::aff[contains(.,"Japan")]
              /parent::article-meta/child::article-id,
    $path2 := $doc/descendant::aff[contains(.,"Japan")]
              /parent::article-meta/child::article-id,
    $path3 := $doc/article/front/article-meta/aff[contains(.,'Japan')]
              /../article-id,
    $path4 := $doc//aff[contains(.,'Japan')]/../article-id,
    $path5 := $doc//aff/../article-id

return (count($path1), count($path2), count($path3), count($path4), count($path5))

What I expect is that path1, path2, path3, path4, and path5 should
all return the same results, namely the set of four article-id elements
in the document.  So the sequence of counts returned should be
4 4 4 4 4.

What I am finding is that path1 and path3 are returning 12 results,
with each article-id present three times in the result (once, apparently,
for every aff element containing the string 'Japan').  Paths 2, 4, and 5
are all returning 4 results each, as I had expected them to.  So
the sequence of counts actually returned is 12 4 12 4 4.

In BaseX 7.6, for what it's worth, this query returns the sequence
12 12 12 12 20, which seems suggestive.

Interestingly, if I initialize the variable $doc with a direct element
constructor, along the lines of

let $doc := document { <article>...</article> }

then all counts come out as expected in 7.6, but in 7.9 the result
continues to be 12 4 12 4 4.

Is this an error in the handling of the / operator, or am I missing some
subtle point?

Many thanks.

[1] http://blackmesatech.com/2014/LIS590DML/data/testdata.xml
--
****************************************************************
* C. M. Sperberg-McQueen, Black Mesa Technologies LLC
* http://www.blackmesatech.com
* http://cmsmcq.com/mib
* http://balisage.net
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