javax.ejb.EJBException: javax.transaction.HeuristicMixedException occurring randomly in batch process

Issue

The following exception is seen in the batch process on most weekends and application crashes as a result.
The problem is random and not easily reproducible.
It occurs in a program with lots of transactions - each time in a different step in the program

javax.ejb.EJBException: javax.transaction.HeuristicMixedException
      at my.example.TransactionHelper.commitTx(TransactionHelper.java:39)
      at my.example.BJR.endBTX(BJR.java:738)
      at my.example.BJP.handleOneBJD(BJP.java:137)
      at my.example.BJP.run(BJP.java:233)
      at my.example.BJR.doWork(BJR.java:276)
      at my.example.BJR.start(BJR.java:1895)
      at my.example.BSBean.processJob(BSBean.java:1246)
      .. .. ..
      at org.jboss.resource.connectionmanager.CachedConnectionInterceptor.invoke(CachedConnectionInterceptor.java:156)
      at org.jboss.ejb.plugins.CallValidationInterceptor.invoke(CallValidationInterceptor.java:63)
      at org.jboss.ejb.plugins.AbstractTxInterceptor.invokeNext(AbstractTxInterceptor.java:121)
      at org.jboss.ejb.plugins.AbstractTxInterceptorBMT.invokeNext(AbstractTxInterceptorBMT.java:173)
      at org.jboss.ejb.plugins.TxInterceptorBMT.invoke(TxInterceptorBMT.java:77)
      at org.jboss.ejb.plugins.StatelessSessionInstanceInterceptor.invoke(StatelessSessionInstanceIn

We are explicitly invoking commit within the transaction block. The commit block looks like

public void commit(Context pContext) {
        Statement statement = null;
        try {
            statement = dbConnection.createStatement();
            statement.executeUpdate("COMMIT");
        } catch (SQLException e) {
            .. .. ..
        } finally {
            close(statement);
        }
    }