possible bug in lxml XMLParser

import sys
import tempfile
from lxml import etree


print("%-20s: %s" % ('Python',           sys.version_info))
print("%-20s: %s" % ('lxml.etree',       etree.LXML_VERSION))
print("%-20s: %s" % ('libxml used',      etree.LIBXML_VERSION))
print("%-20s: %s" % ('libxml compiled',  etree.LIBXML_COMPILED_VERSION))
print("%-20s: %s" % ('libxslt used',     etree.LIBXSLT_VERSION))
print("%-20s: %s" % ('libxslt compiled', etree.LIBXSLT_COMPILED_VERSION))

print
print "parsing with resolve_entities=False, no DOCTYPE"

parser = etree.XMLParser(resolve_entities=False)

try:
    tree = etree.XML("""<test>1<a href="&uuml;bel">&ouml;</a></test>""", parser=parser)
except etree.XMLSyntaxError as e:
    print e

print
print "parsing with resolve_entities=False, dummy DOCTYPE"

try:
    tree = etree.XML("""<!DOCTYPE test SYSTEM ""><test>1<a href="&uuml;bel">&ouml;</a></test>""", parser=parser)
    print tree[:]
    print tree.find('.//a').attrib['href']
    print etree.tostring(tree)
except etree.XMLSyntaxError as e:
    print e



print
print "parsing with actual DOCTYPE declaring the entities"

dtdfile = tempfile.NamedTemporaryFile(suffix='.dtd', delete=False)
dtdfile.write("""<!ELEMENT test (#PCDATA|a)*> <!ELEMENT a (#PCDATA)> <!ATTLIST a href CDATA #REQUIRED> <!ENTITY uuml "&#xfc;"> <!ENTITY ouml "&#xf6;">""")
dtdfile.close()

try:
    tree = etree.XML("""<!DOCTYPE test SYSTEM "{}"><test>1<a href="&uuml;bel">&ouml;</a></test>""".format(dtdfile.name), parser=parser)
    print tree[:]
    print tree.find('.//a').attrib['href']
    print etree.tostring(tree)
except etree.XMLSyntaxError as e:
    print e


print
print "parsing with actual DOCTYPE declaring the entities -- and dtd_validate=True"

parser = etree.XMLParser(resolve_entities=False, dtd_validation=True)
try:
    tree = etree.XML("""<!DOCTYPE test SYSTEM "{}"><test>1<a href="&uuml;bel">&ouml;</a></test>""".format(dtdfile.name), parser=parser)
    print tree[:]
    print tree.find('.//a').attrib['href']
    print etree.tostring(tree)
except etree.XMLSyntaxError as e:
    print e