This is a gap in functionality required by the jaxws spec:

Excerpt from JAX-WS Spec, Section 2.7, p.42:

Additionally, the @XmlType annotation has a propOrder property whose value is an array containing the names of all the properties of the exception class that were mapped in the previous bullet point, sorted lexicographically according to the Unicode value of each of their characters (i.e. using the same algorithm that the int java.lang.String.compareTo(String) method uses).