Duplicate attribute uses, extension, bug in SQC

Hi,

Potential bug in IBM's SQC.
The following schema is accepted by SQC, while the
schema processors Xerces-J 2.7.1, Saxon 8.5.1,
XSV 2.10 and Libxml2 2.6.22 report the attribute use
for "bar" to have a duplicate in the extending complex
type.

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"	
	targetNamespace="urn:test:foo"
	xmlns:f="urn:test:foo">

	<xs:complexType name="base">
		<xs:attribute name="bar"/>
	</xs:complexType>

	<xs:element name="foo">
		<xs:complexType>
			<xs:complexContent>
				<xs:extension base="f:base">
					<xs:attribute name="bar"/>
				</xs:extension>
			</xs:complexContent>
		</xs:complexType>
	</xs:element>

</xs:schema>

Regards,

Kasimier