Schema validator reports the wrong child element as missing

[Bob Kline]

Here's the repro script:

#!/usr/bin/env python3

import sys
from lxml import etree

XSD = """\
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <xsd:element name="Person" type="Person"/>
  <xsd:complexType name="Person">
    <xsd:sequence>
      <xsd:element name="Name" type="xsd:string"/>
      <xsd:element name="Role" type="xsd:string" maxOccurs="2"/>
      <xsd:element name="Detail" type="xsd:string"/>
    </xsd:sequence>
  </xsd:complexType>
</xsd:schema>"""

XML = """\
<Person>
  <Name>Guido</Name>
  <Role>TechnicalBackup</Role>
</Person>"""

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))
schema = etree.XMLSchema(etree.fromstring(XSD))
doc = etree.fromstring(XML)
if not schema.validate(doc):
    print(schema.error_log)

# END OF REPRO SCRIPT

Here's the output:
Python : sys.version_info(major=3, minor=10, micro=6, releaselevel='final', serial=0)
lxml.etree : (4, 9, 1, 0)
libxml used : (2, 9, 14)
libxml compiled : (2, 9, 14)
libxslt used : (1, 1, 35)
libxslt compiled : (1, 1, 35)
<string>:1:0:ERROR:SCHEMASV:SCHEMAV_ELEMENT_CONTENT: Element 'Person': Missing child element(s). Expected is ( Role ).

# END OF OUTPUT

It's clear from examining the schema and the XML document being validated that adding a second Role element is not necessary, and would do nothing to make the document valid. The correct assessment of the validation is that the required Details child element is missing.