xs:choice and xs:sequence question

I have the following complexType coded:

   <xs:complexType name="ProcessingOutcomeMessage">
       <xs:choice>
           <xs:sequence>
               <xs:element ref="DescriptionMessage" minOccurs="0" 
maxOccurs="unbounded" />
               <xs:element ref="MessageReasonCode" minOccurs="0" />
           </xs:sequence>
           <xs:sequence>
               <xs:element ref="DescriptionMessage" type="Description" 
minOccurs="1" maxOccurs="unbounded" />
               <xs:element ref="MessageReasonCode" 
type="MessageReasonCode" minOccurs="1" />
               <xs:element ref="ApplicationReasonCode" 
type="ApplicationReasonCode" minOccurs="1">
                   <xs:annotation>
                       <xs:documentation 
source="http://www.starstandard.org">Contains a software specific 
application reason code.</xs:documentation>
                   </xs:annotation>
               </xs:element>
           </xs:sequence>
       </xs:choice>
   </xs:complexType>

It validates fine if using Xerces J 2.7.0 or XSV 2.5.  However, 
Microsoft's XML, XML Spy 2006 SP2, and Oxygen complain about 
DescriptionMessage being defined twice, even though they are in seperate 
sequence groups.

What I want to do is require DescriptionMessage, MeassageReasonCode if 
there is an ApplicationReasonCode, if there isn't an 
ApplicationReasonCode, then DescriptionMessage and MessageReasonCode are 
optional.

Any help would be appreciated.

Thanks.

Dave