Robert,
I was wondering if you would report the issue that you ran into, with multiple persistence units being used in the quick start application but without specifying the persistence unit name. If you want to get credit for reporting the bug or even helping to fix them (if you want to), the link to report the bug is https://issues.jboss.org/browse/AS7
It might also be worth mentioning that the fix for jira AS7-2275, will prevent applications that have multiple persistence units from using ambigious references to them (unit name will have to be specified for each EntityManager or EntityManagerFactory).
Thanks,
Scott