Do you have copies of your entity bean class in different archives? Like a copy of the Entity bean within your war and another in your par? If so, then you will get CCE's if you only redeploy the .par.
That would explain it, but no: I only have one copy of the entity bean within a single ear. I also tried it with a "clean" JBoss installation; when I drop the ear into the deploy folder, the hot-deployment fails with a NoClassDefFoundError.
Some extra info: the entity is referred from the business interface of a stateless session bean (the interface has a method that takes a parameter of that entity-type.) Actually it's the deployment of the session bean that fails. I checked the session bean-MBean on the JMX-console and it says that it got stuck in "Starting" state...
Does it help at all?