System properties substitution does not work anymore in persistence.xml

In AS6 was possible to use system properties substitution inside the <mapping-file> element. Example:

<persistence-unit name="xyz" transaction-type="JTA">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<jta-data-source>java:/myDS</jta-data-source>
<mapping-file>/META-INF/${drg.db.type}/orm.xml</mapping-file>
<properties>
...
</properties>
</persistence-unit>

The substitution inside the <mapping-file> allows to have different mapping files inside the same application with switching at runtime time and only one artifact.

This stopped working in 7.1.0.Final.