EntityManagerFactory no longer exposes "javax.persistence.nonJtaDataSource"

In Hibernate 4.3.x the following code would return a non-null DataSource:

In Hibernate 5 this no longer appears to work. The EntityManagerFactoryBuilderImpl contains the following line which seems to suggest that the property should be exposed but, as far as I can tell, the configurationValues are no longer copied to the EntityManagerFactory properties. I wonder if instead ssrBuilder.applySetting should now be used?

This issue was originally identified by a Spring Boot user and more background can be found here. The user has also attached a project that replicates the issue when FirstDbConfig and SecondDbConfig are edited to remove his workaround.