JAXB unmarshalling elements with xs:type explicitly set

Question

I am working with XML content where the XSD defines an element as being of a complexType (say "ParentType") but the content explicitly sets the element's xs:type attribute to an extension of that complexType (say "ChildType").
As far as I can tell the XML is valid, but JAXB issues the following when unmarshalling:
DefaultValidationEventHandler: [ERROR]: Unexpected element {}:child1
javax.xml.bind.UnmarshalException: Unexpected element {}:child1
Where <child1> is added via the extension.
Is this a problem with JAXB or my XSD?
(XSD and XML enclosed below)
XSD ------------------
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:complexType name="ParentType">
<xs:sequence>
<xs:element name="parent1" type="xs:string"/>
<xs:element name="parent2" type="xs:string"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="ChildType">
<xs:complexContent>
<xs:extension base="ParentType">
<xs:sequence>
<xs:element name="child1" type="xs:string"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:element name="root">
<xs:complexType>
<xs:sequence>
<xs:element name="child" type="ParentType"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
XML -----------------------
<?xml version="1.0" encoding="UTF-8"?>
<root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="problem.xsd">
<child xsi:type="ChildType">
<parent1/>
<parent2/>
<child1/>
</child>
</root>

Answer 1

JAXB doesn't handle OO schema design. I tried to do something similar where I defined a type called base and then defined that my document contained 1 or more base elements. Then I tried to unmarshall a document that contained elements that were of types extending from base. I ended up with the same issue.
It seems that when the xjc compiler defines the classes it isn't smart enough to realize the element defined as parent could also contain a child element since child extends parent. Your XSD and XML are valid.
I would think that JAXB should identify that because there is a type the extends the defined type, that an element of the sub-type might be subsituted i.e. check the actual type of the element in the XML before attempting to unmarshall it as the default type. It doesn't do that. I am not sure if this is as desinged, or a flaw in the implementation.