Web service response differs from WSDL

Question

Any explanation for this kind of behaviour?

Part of WSDL:

   <complexType name="ArrayCD">
    <sequence>
     <element maxOccurs="unbounded" minOccurs="0" name="item" type="impl:EF"/>
    </sequence>
   </complexType>
   <complexType name="AB">
    <sequence>
     <element name="elem1" nillable="true" type="impl:ArrayCD"/>
    </sequence>
   </complexType>

Part of response from web service method:

<elem1>
 <elem1>
 </elem1>
</elem1>