[xep-support] keep-together + page-number-citation = XEP bug?

The FO below shows a problem I've been having (using XEP 4.6): keep-together.within-line="always" on a fo:inline is not obeyed when there is a <fo:page-number-citation/> inside. The line will not break if the page number is hard-coded, as it is in the first example. But the line will happily break before the page-number-citation inside the keep-together, even though the text content ("on page 1") seems to be the same in both cases.

Am I missing something here? I would really appreciate any suggestions or confirmation (or even denial :-) of the problem.

Thanks,
Stuart

<?xml version="1.0" encoding="iso-8859-1"?>

<fo:root xmlns:fo="http://www.w3.org/1999/XSL/Format">
  <fo:layout-master-set>
    <fo:simple-page-master master-name="my-page">
      <fo:region-body margin="1in"/>
    </fo:simple-page-master>
  </fo:layout-master-set>

  <fo:page-sequence master-reference="my-page">
    <fo:flow flow-name="xsl-region-body">
      <fo:block id="id">This paragraph has the numeral 1 hard-coded:</fo:block>
      <fo:block>blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah <fo:inline keep-together.within-line="always">on page 1</fo:inline></fo:block>
      <fo:block>This paragraph has a page-number-citation:</fo:block>
      <fo:block>blah blah blah blah blah blah blah blah blah blah blah blah blah blah blah <fo:inline keep-together.within-line="always">on page <fo:page-number-citation ref-id="id"/></fo:inline></fo:block>
    </fo:flow>
  </fo:page-sequence>
</fo:root>

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