Some insight please

Hi,
i'm working with Seaside 2.8.2.
In WARegisty>>#unregisterExpiredHandlers at the end of the method it reads: 
  [expired do: [ :each | each unregistered ]] fork.
In turn, WASession>>#unregistered reads like: 
  super unregistered.
  self expire.

So why do expired sessions are sending #expire to theirselves again?
Is there a design reason behind that?

This makes my override MyAppWASession>>#expire to be called twice.
(i explicitly expire my sessions by sending #expire to them but that
doesnt change anything, does it?)

Is it ok if i just override WASession>>#unregistered to not send
expire again?

Greets,
-- vagy