Java Persistence API Spec 188.8.131.52:
"A o/r mapping XML file named orm.xml may be specified in the META-INF directory
in the root of the persistence unit or in the META-INF directory of any jar file
referenced by the persistence.xml. Alternatively, or in addition to, other
mapping files may be referenced by the mapping-file elements of the
persistence-unit element . . . "
Currently, the META-INF/orm.xml is not processed unless explicitly specified
with a mapping-file element of the persistence.xml file. When this workaround
is applied, the descriptors are processed.