Opening a transaction from a Startup Singleton EJB @PostConstruct callback fails

A class like this:

@Startup
@Singleton
public class PopulateDatabase
{
@Resource UserTransaction transaction;

@PostConstruct
public void startup()

{ utx.begin(); ... utx.commit(); ... }

fails with:

BaseTransaction.checkTransactionState - ARJUNA-16051 thread is already associated with a transaction!
at com.arjuna.ats.internal.jta.transaction.arjunacore.BaseTransaction.begin(BaseTransaction.java:65) [:]
at com.arjuna.ats.jbossatx.BaseTransactionManagerDelegate.begin(BaseTransactionManagerDelegate.java:65) [:]
at org.jboss.tm.usertx.client.ServerVMClientUserTransaction.begin(ServerVMClientUserTransaction.java:137) [:]
at org.jboss.weld.examples.pastecode.session.PopulateDatabase.startup(PopulateDatabase.java:94)

at the utx.begin call()