eeff soft
In order to exclude the EntityB form the persistence unit you have to add

<exclude-unlisted-classes>true</exclude-unlisted-classes>

to the <pesistence-unit>
<persistence-unit name="persistenceunitA" transaction-type="RESOURCE_LOCAL">
....
<class>ar.com.eeff.hibernatebugtest.A.TableA</class>
<exclude-unlisted-classes>true</exclude-unlisted-classes>
....
</persistence-unit>
Without

<exclude-unlisted-classes>true</exclude-unlisted-classes> 

Hibernate scans all classes in the root of the Persistence Unit searching for all the annotated managed classes and in your case the second entity you defined TableB has not a corresponding table in the schema databaseA you are connecting to.