Description:
------------
I've created a xml file that uses a doctype to define html entities. I've created an accompanying Relax NG file to validate the file. If the xml element that contains the entity follows an Relax NG <interleave> block, the validation fails. I have demonstrated this in the accompanying source code. The variable $xml is validated against two Relax NG schemas, where the preceding elements are contained in an <interleave> block, and one where the are not. The validation fails in the <interleave> case.

I have tried the validation using an online validator (java based, uses jing), see:
http://hsivonen.iki.fi/validator/
so it is not the XML or the Relax NG, but rather the validator itself.

I have found other circumstances where the presence entities cause the validation to fail, I can provided these if they are necessary.

Reproduce code:
---------------
<?php

$xml = <<<EOF
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE root[
  <!ENTITY mu "mu">
]>
<eec:field xmlns:eec="http://www.triumf.info/common/xml/eec"
          xmlns="http://www.w3.org/1999/xhtml">

    <eec:title>Isotope</eec:title>
    <eec:name>sec_isotope</eec:name>
    <eec:type>text</eec:type>
    <eec:value>&mu;</eec:value>
</eec:field>
EOF;

$rng = <<<EOF
<?xml version="1.0" encoding="UTF-8"?>

<grammar xmlns="http://relaxng.org/ns/structure/1.0"
         xmlns:eec="http://www.triumf.info/common/xml/eec">
         
  <start>
    <element name="eec:field">
      <interleave>
      <element name="eec:title"><text/></element>
      <element name="eec:name"><text/></element>
      <element name="eec:type"><text/></element>
      </interleave>
      <element name="eec:value"><text/></element>
    </element>
  </start>
    
</grammar>
EOF;

$rng2 = <<<EOF
<?xml version="1.0" encoding="UTF-8"?>

<grammar xmlns="http://relaxng.org/ns/structure/1.0"
         xmlns:eec="http://www.triumf.info/common/xml/eec">
         
  <start>
    <element name="eec:field">
      <element name="eec:title"><text/></element>
      <element name="eec:name"><text/></element>
      <element name="eec:type"><text/></element>
      <element name="eec:value"><text/></element>
    </element>
  </start>
    
</grammar>
EOF;

ini_set( 'track_errors', 1);
ini_set('error_reporting', E_ALL | E_STRICT);

$dom = new DOMDocument();
$dom->loadXML($xml, LIBXML_DTDLOAD|LIBXML_DTDATTR);

echo "<h3>1st Time</h3>";
if ($dom->relaxNGValidateSource($rng)) echo "Relax NG validated";
else echo $php_errormsg;

echo "<h3>2nd Time</h3>";
if ($dom->relaxNGValidateSource($rng2)) echo "Relax NG validated";
else echo $php_errormsg;
?> 

Expected result:
----------------
1st Time
Relax NG validated
2nd Time
Relax NG validated

Actual result:
--------------
1st Time
Element value has extra content: mu
2nd Time
Relax NG validated