¿Y en cabeza sí te funciona?
Si tampoco funciona, yo diría que depende de cómo esté definido el xsd.
http://www.w3schools.com/schema/el_schema.asp Cita: elementFormDefault
Optional. The form for elements declared in the target namespace of this schema. The value must be "qualified" or "unqualified". Default is "unqualified". "unqualified" indicates that elements from the target namespace are not required to be qualified with the namespace prefix. "qualified" indicates that elements from the target namespace must be qualified with the namespace prefix