This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
The idea of the SUIDis that when you have two instances of the same class with the same SUID, the JVM assumes they are from the same class object. If you have different SUIDs, the JVM may assume they are from different versions of the class, and the objects may not be de-serialized.
And I agree it is very peculiar to have two definitions in the same class.