DOMDocument::schemaValidate() - group nodes inside choice nodes

here's a simple schema and document that illustrates my problem- for the
life of me i cannot see why this document is not valid against the schema.
i simplified it a lot- i do need to use the group tag because customer-info
contains a lot more than just a name.

DOMDocument::schemaValidate() method says this is invalid.  BUT if i cut the
customer-info group and paste it over top of <xs:group ref="customer-info"/>
... then everything is fine!?!  now, this is a (big) stretch but- could it
be a bug in schemaValidate()?

Schema:
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xs:element name="customer">
        <xs:complexType>
            <xs:choice>
                <xs:element ref="customer-id"/>
                <xs:group ref="customer-info"/>
            </xs:choice>
        </xs:complexType>
    </xs:element>

    <xs:element name="customer-id" type="xs:long" />

    <xs:group name="customer-info">
        <xs:sequence>
            <xs:element ref="name" minOccurs="1" maxOccurs="1"/>
            <xs:element ref="
        </xs:sequence>
    </xs:group>
</xs:schema>

 XML document:
<customer>
        <name>Bob Eubanks</name>
</customer>