Instances of processes showing the console are on the table processInstanceLog, see if the table is empty when you reboot the server.
In the original persistance.xml and persistance_human_task.xml the hibernate.hbm2ddl.auto property is create.
When you restart the server processes the tables are created again, so do not time the process instance.
The tasks related tables are created again when you run ant start.human.task.
So if you restart the server and not restart the human task service the data are inconsistent.
The link can help you
http://community.jboss.org/message/589323 # 589323
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