XSLT 2.0 and implementation of fn:idref in Saxon 7.9

Hello,

I just tested the fn:idref function with saxon 7.9 but I got a very
unexpected result:
----------- the xml -------------
<?xml version="1.0" encoding="utf-8"?>
   <!DOCTYPE data [
      <!ATTLIST event
        id   ID #REQUIRED
        name CDATA #REQUIRED >
      <!ATTLIST participant
        name CDATA #REQUIRED
        events IDREFS #REQUIRED >
   ]>
<data>
  <events>
     <event id="e01" name="Amsterdam"/>
     <event id="e02" name="Baltimore"/>
     <event id="e03" name="Casablanca"/>
  </events>
  <participants>
    <participant events="e01 e03" name="Alpha"/>
    <participant events="e02" name="Bravo"/>
    <participant events="e02 e03" name="Charlie"/>
  </participants>
</data>

-------- xslt (important part) -------------------
<xsl:template match="participant">
 <h3><xsl:value-of select="@name"/></h3>
 	<xsl:copy-of select="id(@events)" />
	<ul>
	    <xsl:apply-templates select="id(@events)" mode="byparticipant"/>
	</ul>
</xsl:template>
<xsl:template match="event" mode="byparticipant">
 <li><xsl:value-of select="@name"/></li>
</xsl:template>

<xsl:template match="event">
	<h3><xsl:value-of select="@name"/></h3>
	<xsl:copy-of select="idref(@id)" />
    <ul>
        <xsl:apply-templates select="idref(@id)" mode="byevent"/>
    </ul>
</xsl:template>
<xsl:template match="participant" mode="byevent">
    <li><xsl:value-of select="@name"/></li>
</xsl:template>

---------------- resul by saxon 7.9 -------------
Warning:  Cannot write an attribute node when no element start tag is
open

      <h3>Alpha</h3>
      <event id="e01" name="Amsterdam"></event>
      <event id="e03" name="Casablanca"></event>
      <ul>
         <li>Amsterdam</li>
         <li>Casablanca</li>
      </ul>

      <h3>Bravo</h3>
      <event id="e02" name="Baltimore"></event>
      <ul>
         <li>Baltimore</li>
      </ul>

      <h3>Charlie</h3>
      <event id="e02" name="Baltimore"></event>
      <event id="e03" name="Casablanca"></event>
      <ul>
         <li>Baltimore</li>
         <li>Casablanca</li>
      </ul>


      <h3>Amsterdam</h3>
      <ul>e01 e03</ul>

      <h3>Baltimore</h3>
      <ul>e02e02 e03</ul>

      <h3>Casablanca</h3>
      <ul>e01 e03e02 e03</ul>

----------------------------------------------------------

Did I misunterstand the meaning of the fn:idref (Finds the elements that
link to the element with a given ID value i.e. This function allows
reverse navigation from IDs to IDREFs.) ?

Regards
Thomas

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