AnyNode changing namespace prefix to first one encountered for sibling nodes (if the namespace uri is reused). If AnyNode has the following XML <f:firstname xmlns:f="http://name.namespace"> <f:text>John</f:text> </f:firstname> <l:lastname xmlns:l="http://name.namespace" > <l:text>Right</l:text> </l:lastname> The namespace after unmarshalling & marshalling for the second node (re-using namespace URI but a different prefix) is changed to the namespace prefix of the first one i.e. After an unmarshall and marshall, the resulting XML will be <f:firstname xmlns:f="http://name.namespace"> <f:text>John</f:text> </f:firstname> <!-- Note the change here, the XML is invalid now --> <f:lastname xmlns:l="http://name.namespace"> <f:text>Right</f:text> </f:lastname> The marshalled XML now has "f:lastName" with namespace declaration of "xml:l", resulting in INVALID XML.