xsi:type handling

All,

I have a derived type from short in my schema such as:

     <xs:simpleType name="MyDerivedFromShortType">
         <xs:restriction base="xs:short">
             <xs:minInclusive value="1"/>
             <xs:maxInclusive value="100"/>
         </xs:restriction>
     </xs:simpleType>

My question now is, if following line in a instance document is valid?

        <ns2:MyDerivedFromShort
xsi:type="xsd:short">99</ns2:MyDerivedFromShort>

When parsing this with Xerces it will throw

Validation error: LineNumber: 48 ColumnNumber: 2883 Message: 
cvc-elt.4.3: Type 'xsd:short' is not validly derived from the type 
definition, 'MyDerivedFromShortType', of element
'ns2:MyDerivedFromShort'.:

Can someone confirm that Xerces' behaviour is reasonable?

Thanks
Yves