[xml] libxml2: bug in most recent CygWin version?

[Mike Maxwell <maxwell ldc upenn edu>]

I'm getting an odd error msg when I run xmllint on one of my XML files. 
I suspect it's a bug.  I'm a newby at XML etc., but (1) I  didn't get 
this msg running xmllint on CygWin before (when I presumably had an 
earlier version of xmllint/ libxml2), and (2) I still don't get this msg 
when I run xmllint on a FreeBSD system (which has an older version of 
these programs).

Specifically, the use of an entity defined in an XML file triggers the 
following when I run
  xmllint --noout --schema ParadigmDefn.xsd TestSuite/Paradigms.Defn.xml
on the CygWin version:

---------
Unimplemented block at 
/instsoft/libxml/uploaded/libxml2-2.6.20/xmlschemas.c:23832
Element 
'{http://lodl.ldc.upenn.edu/ParadigmDefn.xsd}DisallowedFeatureValues':
Element content is not allowed, because the type definition is simple.
TestSuite/Paradigms.Defn.xml fails to validate
---------

When I run xmllint --version on CygWin, I get the ff.:

---------
xmllint: using libxml version 20620
   compiled with: DTDValid FTP HTTP HTML C14N Catalog XPath XPointer 
XInclude Ic
onv Unicode Regexps Automata Schemas Modules
---------

These same files used to pass xmllint fine, and they still do when I run 
xmllint on a FreeBSD system.  The FreeBSD libxml uses a slightly older 
version of libxml:

---------
xmllint: using libxml version 20619
   compiled with: DTDValid FTP HTTP HTML C14N Catalog XPath XPointer 
XInclude Iconv Unicode Regexps Automata Schemas
---------

The xsd in question is too large to post in this msg, but here's a sort 
of minimal XML file that will trigger the error:

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

<!DOCTYPE ParadigmDefn
    [ <!ENTITY Clitic2 "foobar"> ]
>

<ParadigmDefns xmlns ="http://lodl.ldc.upenn.edu/ParadigmDefn.xsd";
                         xmlns:xsi 
="http://www.w3.org/2001/XMLSchema-instance";
                         xsi:schemaLocation="http://lodl.ldc.upenn.edu 
ParadigmDefn.xsd"
                         Title="Paradigms"
>
    <POS category="V0">
        <Paradigm name="tenses" constant_features="3sgS-">
            <FeatureValueSet >
                <DisallowedFeatureValues> &Clitic2; 
</DisallowedFeatureValues>
            </FeatureValueSet>
        </Paradigm>
    </POS>
</ParadigmDefns>
---------

Substituting the value for the entity (i.e. <DisallowedFeatureValues> 
"foobar" </DisallowedFeatureValues>) results in the above XML passing 
xmllint.

Is this a bug?  Or am I doing s.t. wrong?
--
        Mike Maxwell
        Linguistic Data Consortium
        maxwell ldc upenn edu

        "When I get a little money I buy books;
          and if any is left I buy food and clothes."
        --Erasmus