A bug or incorrect logic?

I have a complex-type defined as follows:

<xsd:complexType name="PersonNameType">
	<xsd:sequence>
             <xsd:element name="PersonPrefixName" 
type="PersonPrefixNameType" minOccurs="0" maxOccurs="1"/>
             <xsd:choice>
                 <xsd:element name="PersonFirstName" 
type="PersonGivenNameType" minOccurs="1" maxOccurs="1"/>
                 <xsd:element name="PersonGivenName" 
type="PersonGivenNameType" minOccurs="1" maxOccurs="1"/>
             </xsd:choice>
             <xsd:element name="PersonMiddleName" 
type="PersonMiddleNameType" minOccurs="0" maxOccurs="1"/>
             <xsd:choice>
                 <xsd:element name="PersonLastName" 
type="PersonSurNameType" minOccurs="1" maxOccurs="1"/>
                 <xsd:element name="PersonSurName" 
type="PersonSurNameType" minOccurs="1" maxOccurs="1"/>
             </xsd:choice>
             <xsd:element name="PersonSuffixName" 
type="PersonSuffixNameType" minOccurs="0" maxOccurs="1"/>
             <xsd:element name="PersonMaidenName" 
type="PersonMaidenNameType" minOccurs="0" maxOccurs="1"/>
             <xsd:element name="PersonFullName" 
type="PersonFullNameType" minOccurs="0" maxOccurs="1"/>
         </xsd:sequence>
</xsd:complexType>

When testing with an instance where the SignerName element
is of type PersonNameType, and is deliberately kept empty
(as follows):

  <SignerName/>

the XML Schema tool gives me the following error:

cvc-complex-type.2.4.b: The content of element 'SignerName' is not 
complete. One of '{PersonPrefixName, PersonFirstName, PersonGivenName}' 
is expected. [129]

However, the PersonPrefixName has a minOccurs of "0", so
why am I seeing an error where the tool insists that the
PersonPrefixName is expected?

Thanks.

Arshad Noor
StrongAuth, Inc.