This has all been documented in urls listed below:
   QUARTZ-421
   http://forums.opensymphony.com/thread.jspa?messageID=87626&#87626

But to sum it up without forcing you to read those other urls.....

When a Job with no JobData is serialized to the db, it is serialized as an empty byte array (ie. new byte[0]). This seems to work without error, but when deserializing that Job a JobPersistenceException (wrapping a EOFException ) is thrown. A little investigation shows that StdJDBCDelegate.getObjectFromBlob takes the InputStream it receives from the database and calls .readObject against it via an ObjectInputStream. For empty byte arrays this results in the EOFException.

I could see this this being a problem for situations other than Jobs with empty JobData, but I'll leave that as an exercise for the committers ;-)

Thanks!