All classes that are likely to be cached should be immutable.
Cached objects that are immutable can cause weird problems, if references are updated after the object has been cached. Instead, use immutable objects (the JCIP annotations can help here).
As a bonus, we will prevent most concurrency-related problems when we make stuff immutable.
This is a generic Good Idea© but not something that requires explicit action.
Guus, do you have a current comment on this issue?
Is this ticket still valid given the recent cluster updates in 3.8.0 ?