Doubt about validation

Dear xmlschema-dev,

I have a subtle problem. I just uploaded the attached XSD schema file to http://www.w3.org/2000/06/webdata/xsv to be sure the schema is valid, and your validator says that all is OK.

But when I use the schema to validate the XML document also attached I get an error, from any of the available parsers (not from all); in particular:
    Xerces C++,      error
    MSXML 4.0,      no error
    XMLSpy 4.x,     no error
    .NET (System.Xml),  error

The error seems to be in the definition af the type "typeparametersyntax":
<xs:complexType name="typeparametersyntax">
  <xs:annotation>
    <xs:documentation>
      Fixed text and/or variable data but not empty!
    </xs:documentation>
  </xs:annotation>
  <xs:choice>
    <xs:element name="Text" type="xs:string"/>
    <xs:sequence>
      <xs:element name="Text" type="xs:string"/>
      <xs:element ref="data"/>
    </xs:sequence>
    <xs:element ref="data"/>
  </xs:choice>
</xs:complextype>

the parsers that report error claim for non-deterministic content model (not so clearly, however!).

Why your parser doesn't report any error ?
Can you give me any suggestion to solve the problem ?

Thank you in advance.

Santino